title
Arrays and Sorting Algorithms - Intro to Computer Science - Harvard's CS50 (2018)

description
Learn about arrays, strings, and sorting algorithms and how they work in the C programming language. This course teaches the foundations of computer science. This video is lecture 2 of Harvard University's CS50 2018 course (part 3 since the lectures start at 0). Check out our full CS50 playlist: https://www.youtube.com/playlist?list=PLWKjhJtqVAbmGw5fN5BQlwuug-8bDmabi 🔗Notes: https://cs50.harvard.edu/x/2020/notes/2/ 🔗Problem Set: https://cs50.harvard.edu/x/2020/psets/2/ 🔗Source Code: https://cdn.cs50.net/2019/fall/lectures/2/src2.zip ⭐️Contents⭐️ ⌨️ (00:00:00) Introduction ⌨️ (00:00:54) Week 1 Recap ⌨️ (00:04:47) Preprocessing ⌨️ (00:07:05) Compiling ⌨️ (00:09:01) Assembling ⌨️ (00:09:29) Linking ⌨️ (00:12:36) buggy0.c ⌨️ (00:16:13) buggy2.c ⌨️ (00:25:14) Debugging Tools ⌨️ (00:26:02) RAM ⌨️ (00:29:11) Arrays ⌨️ (00:30:01) scores0.c ⌨️ (00:41:47) scores2.c ⌨️ (00:49:45) scores4.c ⌨️ (00:52:21) string0.c ⌨️ (01:00:42) Null Terminator ⌨️ (01:03:06) strlen.c ⌨️ (01:06:16) ascii0.c ⌨️ (01:09:39) capitalize0.c ⌨️ (01:12:23) capitalize1.c ⌨️ (01:16:38) argv0.c ⌨️ (01:21:25) argv1.c ⌨️ (01:24:52) Ciphering ⌨️ (01:33:15) exit.c ⌨️ (01:36:58) Finding 50 ⌨️ (01:40:38) Sorting on Stage ⌨️ (01:50:27) Bubble Sort ⌨️ (01:51:34) Selection Sort ⌨️ (01:52:23) Computational Complexity ⌨️ (01:57:42) Merge Sort ⌨️ (02:04:29) Comparing Sorts Visually Lecture taught by David J. Malan. Thanks to Harvard's CS50 for giving us permission to post this lecture. Checkout their YouTube channel for more great lectures: https://www.youtube.com/cs50 -- Learn to code for free and get a developer job: https://www.freecodecamp.org Read hundreds of articles on programming: https://medium.freecodecamp.org

detail
{'title': "Arrays and Sorting Algorithms - Intro to Computer Science - Harvard's CS50 (2018)", 'heatmap': [{'end': 7595.317, 'start': 7418.809, 'weight': 0.725}], 'summary': 'Covers transitioning to c, c compilation process, computer hardware, memory, arrays, functions, string manipulation, character manipulation, cryptography, and sorting algorithms. it emphasizes the significance of each topic and provides insights for efficient programming.', 'chapters': [{'end': 256.66, 'segs': [{'end': 106.252, 'src': 'embed', 'start': 68.811, 'weight': 4, 'content': [{'end': 71.473, 'text': 'But the ideas, recall, were fundamentally the same.', 'start': 68.811, 'duration': 2.662}, {'end': 73.915, 'text': "The catch is that computers don't understand this.", 'start': 71.553, 'duration': 2.362}, {'end': 79.034, 'text': 'They only understand what language? Yeah, 0s and 1s are binary.', 'start': 73.975, 'duration': 5.059}, {'end': 84.017, 'text': "And so there's a requisite step in order for us to get from this code to binary.", 'start': 79.074, 'duration': 4.943}, {'end': 89.081, 'text': 'And what was that step or that program or process called? Yeah, so compiling.', 'start': 84.177, 'duration': 4.904}, {'end': 94.944, 'text': "And of course, recall, as you've now experimented with this past week, that to compile a program, you can use Clang for C language.", 'start': 89.121, 'duration': 5.823}, {'end': 97.706, 'text': 'And you can just say Clang and then the name of the file that you want to compile.', 'start': 94.964, 'duration': 2.742}, {'end': 103.57, 'text': 'And that outputs by default a pretty oddly named program, just a.out, which stands for assembler output.', 'start': 97.726, 'duration': 5.844}, {'end': 104.751, 'text': 'More on that in just a moment.', 'start': 103.69, 'duration': 1.061}, {'end': 106.252, 'text': 'But recall, too, that.', 'start': 105.111, 'duration': 1.141}], 'summary': 'Computers understand binary (0s and 1s) through compiling, such as using clang for c language, which produces a default program named a.out.', 'duration': 37.441, 'max_score': 68.811, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I68811.jpg'}, {'end': 148.04, 'src': 'embed', 'start': 122.87, 'weight': 0, 'content': [{'end': 131.333, 'text': 'It compiles it and it essentially figures out all of those otherwise cryptic-looking command line arguments like dash o something and so forth,', 'start': 122.87, 'duration': 8.463}, {'end': 136.895, 'text': 'so that the program is built just the way we want it, without our having to remember those seemingly magical incantations.', 'start': 131.333, 'duration': 5.562}, {'end': 140.836, 'text': 'that only works for programs as simple as this.', 'start': 138.115, 'duration': 2.721}, {'end': 141.177, 'text': 'In fact,', 'start': 140.877, 'duration': 0.3}, {'end': 148.04, 'text': 'some of you with the most recent problem set might have encountered compilation errors that we actually did not encounter deliberately in class,', 'start': 141.177, 'duration': 6.863}], 'summary': 'The compiler simplifies command line arguments for program building, but may not work for more complex programs.', 'duration': 25.17, 'max_score': 122.87, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I122870.jpg'}, {'end': 200.642, 'src': 'embed', 'start': 155.874, 'weight': 1, 'content': [{'end': 163.567, 'text': "h, Some of you might have realized that all of a sudden the sandbox, and more generally Clang, didn't know what get string was.", 'start': 155.874, 'duration': 7.693}, {'end': 165.988, 'text': 'And frankly, Clang might not even known what a string was.', 'start': 163.627, 'duration': 2.361}, {'end': 171.851, 'text': "And that's because those two are features of CS50's library that you have to teach Clang about.", 'start': 166.308, 'duration': 5.543}, {'end': 176.822, 'text': "But it's not enough to teach Clang what they look like as by including CS50.", 'start': 172.111, 'duration': 4.711}, {'end': 184.715, 'text': "h Turns out there's a missing step that make helps us solve, but that you too can just solve manually if you want.", 'start': 176.822, 'duration': 7.893}, {'end': 186.116, 'text': 'And by that, I mean this.', 'start': 184.975, 'duration': 1.141}, {'end': 190.178, 'text': 'Instead of compiling a program with just Clang hello.c.', 'start': 186.596, 'duration': 3.582}, {'end': 197.26, 'text': "when you want to use CS50's library, you actually need to add this additional command line argument specifically at the end.", 'start': 190.178, 'duration': 7.082}, {'end': 199.301, 'text': "Can't go in the beginning like dash o.", 'start': 197.34, 'duration': 1.961}, {'end': 200.642, 'text': 'And dash l stands for link.', 'start': 199.301, 'duration': 1.341}], 'summary': "Teaching clang about cs50's library requires adding a specific command line argument at the end of the program compilation.", 'duration': 44.768, 'max_score': 155.874, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I155874.jpg'}], 'start': 0.571, 'title': "Transitioning to c and using cs50's library", 'summary': "Covers the transition from graphical programming to c, the importance of compiling, using clang and make utility, and the process of using cs50's library with clang, providing insights into simplifying program building and the additional command line argument required.", 'chapters': [{'end': 141.177, 'start': 0.571, 'title': 'Cs50 week 2: from graphical programming to c', 'summary': 'Discusses the transition from building a graphical programming language to c, the importance of compiling, using clang and make utility for compiling programs, and the convenience of make utility in simplifying command line arguments for program building.', 'duration': 140.606, 'highlights': ['Computers understand only 0s and 1s, requiring a requisite step from code to binary, known as compiling.', 'To compile a C program, Clang can be used, and the default output is a program named a.out.', 'Using make utility simplifies the process of compiling by automatically figuring out command line arguments for program building.']}, {'end': 256.66, 'start': 141.177, 'title': "Using cs50's library with clang", 'summary': "Discusses the process of using cs50's library with clang, including the need to teach clang about the features of the library and the additional command line argument required for compiling programs using cs50's library.", 'duration': 115.483, 'highlights': ["The need to teach Clang about the features of CS50's library Teaching Clang about the features of CS50's library, such as get string, is essential for successful compilation.", "The additional command line argument required for using CS50's library with Clang Adding the command line argument -lcs50 at the end of the compilation command is necessary to link CS50's library with the program, resolving issues with undefined reference errors.", "Automation of the process using make The make command automates the process of linking CS50's library with the program, making the compilation process more efficient and less tedious."]}], 'duration': 256.089, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I571.jpg', 'highlights': ['Using make utility simplifies the process of compiling by automatically figuring out command line arguments for program building.', "The make command automates the process of linking CS50's library with the program, making the compilation process more efficient and less tedious.", "The additional command line argument required for using CS50's library with Clang Adding the command line argument -lcs50 at the end of the compilation command is necessary to link CS50's library with the program, resolving issues with undefined reference errors.", "The need to teach Clang about the features of CS50's library Teaching Clang about the features of CS50's library, such as get string, is essential for successful compilation.", 'To compile a C program, Clang can be used, and the default output is a program named a.out.', 'Computers understand only 0s and 1s, requiring a requisite step from code to binary, known as compiling.']}, {'end': 1544.746, 'segs': [{'end': 315.36, 'src': 'embed', 'start': 286.87, 'weight': 0, 'content': [{'end': 290.693, 'text': "in hopes that it makes the code we're compiling a little more understandable.", 'start': 286.87, 'duration': 3.823}, {'end': 292.735, 'text': 'So step one of four.', 'start': 291.073, 'duration': 1.662}, {'end': 296.156, 'text': 'when it comes to actually compiling a program is called preprocessing.', 'start': 293.095, 'duration': 3.061}, {'end': 300.497, 'text': 'So recall that this program we just looked at had a couple of includes at the top of the file.', 'start': 296.376, 'duration': 4.121}, {'end': 303.137, 'text': 'These are generally known as preprocessor directives.', 'start': 300.797, 'duration': 2.34}, {'end': 308.798, 'text': "Not a particularly interesting term, but they're demarcated by the hash at the start of these lines.", 'start': 303.237, 'duration': 5.561}, {'end': 315.36, 'text': "That's a signal to Clang that these things should be handled first, preprocessed, processed before everything else.", 'start': 308.858, 'duration': 6.502}], 'summary': 'Preprocessing in compiling involves handling preprocessor directives signaled by a hash, to make the code more understandable.', 'duration': 28.49, 'max_score': 286.87, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I286870.jpg'}, {'end': 356.977, 'src': 'embed', 'start': 327.951, 'weight': 1, 'content': [{'end': 330.471, 'text': "So there's some lines of code, the prototype,", 'start': 327.951, 'duration': 2.52}, {'end': 338.152, 'text': 'if you recall that one line of code that teaches Clang what the inputs to get string are and what the outputs are, the return type and the arguments,', 'start': 330.471, 'duration': 7.681}, {'end': 338.672, 'text': 'so to speak.', 'start': 338.152, 'duration': 0.52}, {'end': 340.993, 'text': 'And so when you have include CS50.', 'start': 338.953, 'duration': 2.04}, {'end': 342.693, 'text': 'h at the top of the file.', 'start': 340.993, 'duration': 1.7}, {'end': 346.734, 'text': "what's happening when you first run Clang during this so-called preprocessing step?", 'start': 342.693, 'duration': 4.041}, {'end': 349.674, 'text': 'is Clang looks on the hard drive for the file, literally called CS50..', 'start': 346.734, 'duration': 2.94}, {'end': 355.036, 'text': 'h It grabs its content and essentially finds and replaces this line here.', 'start': 349.674, 'duration': 5.362}, {'end': 356.977, 'text': 'So somewhere in CS50.', 'start': 355.336, 'duration': 1.641}], 'summary': 'Teaching clang about input and output types through one line of code, preprocessing step in clang involves finding and replacing content.', 'duration': 29.026, 'max_score': 327.951, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I327951.jpg'}, {'end': 573.11, 'src': 'embed', 'start': 547.613, 'weight': 4, 'content': [{'end': 555.017, 'text': 'So the third step is actually to convert this assembly language to actual 0s and 1s that now look like this.', 'start': 547.613, 'duration': 7.404}, {'end': 557.979, 'text': 'So the assembling step happening unbeknownst to you.', 'start': 555.578, 'duration': 2.401}, {'end': 560.32, 'text': 'every time you run clang or in turn run, make,', 'start': 557.979, 'duration': 2.341}, {'end': 565.203, 'text': "we're getting 0s and 1s out of the assembly code and we're getting the assembly code out of your C code.", 'start': 560.32, 'duration': 4.883}, {'end': 568.848, 'text': "But here's the fourth and final step.", 'start': 565.987, 'duration': 2.861}, {'end': 573.11, 'text': "Recall that we need to link in other people's 0s and 1s.", 'start': 569.309, 'duration': 3.801}], 'summary': "Convert assembly language to 0s and 1s, and link in other people's 0s and 1s.", 'duration': 25.497, 'max_score': 547.613, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I547613.jpg'}, {'end': 615.084, 'src': 'embed', 'start': 589.258, 'weight': 2, 'content': [{'end': 595.916, 'text': 'And it happens to use a couple of other libraries files that other people wrote of useful code for you, like cs50..', 'start': 589.258, 'duration': 6.658}, {'end': 601.393, 'text': 'c, which does exist somewhere, and even standardio.c, which does exist somewhere.', 'start': 595.916, 'duration': 5.477}, {'end': 606.999, 'text': 'Or technically, standardio is such a big library, they actually put printf in a file specifically called printf.c.', 'start': 601.473, 'duration': 5.526}, {'end': 615.084, 'text': 'But somewhere in the sandboxes, hard drive, and all of our Macs and PCs, if they support compiling, are, for instance, files like these.', 'start': 607.72, 'duration': 7.364}], 'summary': 'Libraries like cs50.c and standardio.c provide useful code for compiling on macs and pcs.', 'duration': 25.826, 'max_score': 589.258, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I589258.jpg'}, {'end': 975.954, 'src': 'embed', 'start': 951.081, 'weight': 5, 'content': [{'end': 956.242, 'text': "If on first glance you don't really understand what an error message is doing, even though you've scrolled to the very first one,", 'start': 951.081, 'duration': 5.161}, {'end': 959.983, 'text': 'like literally ask this program for help by rerunning the exact same command.', 'start': 956.242, 'duration': 3.741}, {'end': 963.464, 'text': 'you just ran, but prefix it with help 50 and a space.', 'start': 959.983, 'duration': 3.481}, {'end': 965.464, 'text': 'And that will run help 50 for you.', 'start': 963.884, 'duration': 1.58}, {'end': 975.954, 'text': "Any questions on that process? All right, let's take a look at one other program, for instance, that this time has a different error involved in it.", 'start': 965.865, 'duration': 10.089}], 'summary': "When encountering an unclear error message, rerun the command with 'help 50' to seek assistance. additional program examples with different errors are also discussed.", 'duration': 24.873, 'max_score': 951.081, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I951081.jpg'}, {'end': 1241.025, 'src': 'embed', 'start': 1211.526, 'weight': 9, 'content': [{'end': 1213.969, 'text': 'When in doubt, literally use printf.', 'start': 1211.526, 'duration': 2.443}, {'end': 1216.151, 'text': 'on this line, on this line, on this line.', 'start': 1214.429, 'duration': 1.722}, {'end': 1219.256, 'text': 'Anywhere. something is interesting maybe going on in your program.', 'start': 1216.292, 'duration': 2.964}, {'end': 1221.539, 'text': 'just use it to print out the strings that are in your variables.', 'start': 1219.256, 'duration': 2.283}, {'end': 1224.983, 'text': 'print out the integers that are in your variables, or anything else.', 'start': 1221.539, 'duration': 3.444}, {'end': 1230.29, 'text': "And it allows you to kind of see, so to speak, what's going on inside of your program.", 'start': 1225.003, 'duration': 5.287}, {'end': 1234.123, 'text': 'Printf All right, one last tool.', 'start': 1231.192, 'duration': 2.931}, {'end': 1241.025, 'text': "So it's not uncommon when writing code to maybe get a little sloppy early on, especially when you're not quite familiar with the patterns.", 'start': 1234.484, 'duration': 6.541}], 'summary': 'Use printf to print out strings and integers for program insight.', 'duration': 29.499, 'max_score': 1211.526, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I1211526.jpg'}, {'end': 1544.746, 'src': 'embed', 'start': 1510.232, 'weight': 8, 'content': [{'end': 1516.734, 'text': "so just to recap, then three tools to have in the proverbial tool block now are help 50, any time you see an error message that you don't understand,", 'start': 1510.232, 'duration': 6.502}, {'end': 1519.095, 'text': "whether it's with make or clang or perhaps something else.", 'start': 1516.734, 'duration': 2.361}, {'end': 1521.775, 'text': "Printf when you've got a logical program,", 'start': 1519.435, 'duration': 2.34}, {'end': 1527.037, 'text': "a bug in your program and it's just not working the way it's supposed to or the way the problem set tells you it should.", 'start': 1521.775, 'duration': 5.262}, {'end': 1533.979, 'text': 'And then style 50, when you want to make sure that, does my code look right in terms of style and is it as readable as possible?', 'start': 1527.397, 'duration': 6.582}, {'end': 1537.1, 'text': "And honestly, you'll find us at office hours and the like, often encouraging you.", 'start': 1534.039, 'duration': 3.061}, {'end': 1540.723, 'text': 'Before we answer this question, can you please run style 50 on your code?', 'start': 1537.68, 'duration': 3.043}, {'end': 1542.184, 'text': 'Can you please clean up your code?', 'start': 1540.923, 'duration': 1.261}, {'end': 1544.746, 'text': 'Because it just makes our lives too, as other humans,', 'start': 1542.224, 'duration': 2.522}], 'summary': 'Key tools for problem-solving: help50, printf, style50. encouraged at office hours.', 'duration': 34.514, 'max_score': 1510.232, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I1510232.jpg'}], 'start': 256.66, 'title': 'C compilation process and debugging', 'summary': "Delves into the c compilation process, covering preprocessing, compiling, assembling, and linking, and introduces debugging techniques such as 'help 50' for troubleshooting errors and the use of printf for diagnostics. it emphasizes the significance of each step in the compilation process and provides insights into identifying and fixing bugs in c code.", 'chapters': [{'end': 400.577, 'start': 256.66, 'title': 'Compiling process and preprocessing', 'summary': 'Discusses the preprocessing step in the compilation process, highlighting the role of preprocessor directives and the handling of included files, providing a deeper understanding of the code compilation.', 'duration': 143.917, 'highlights': ['The preprocessing step in the compilation process involves handling preprocessor directives demarcated by a hash, which are processed before everything else.', 'During the preprocessing step, Clang looks for included files on the hard drive and replaces specific lines of code, such as function declarations and definitions, from those files.', "Included files like CS50.h and standardio.h contain function declarations, such as get string and printf, which are essential for the program's functionality."]}, {'end': 829.973, 'start': 400.617, 'title': 'Understanding c compilation process', 'summary': 'Explains the c compilation process, including preprocessing, compiling, assembling, and linking, where the code is transformed from c to assembly language, then to machine code, and linked with other libraries to produce the final executable, with an emphasis on the importance of each step and the significance of assembly and machine code, and it also introduces troubleshooting techniques for identifying and fixing bugs in c code.', 'duration': 429.356, 'highlights': ['The chapter explains the C compilation process, including preprocessing, compiling, assembling, and linking, emphasizing the importance of each step.', 'It explains how the code is transformed from C to assembly language, then to machine code, and linked with other libraries to produce the final executable.', 'It introduces troubleshooting techniques for identifying and fixing bugs in C code, including the importance of including the header file for the library functions, such as printf.']}, {'end': 1062.239, 'start': 830.193, 'title': 'Using help 50 for debugging', 'summary': "Explains how to use the 'help 50' command, created by the staff, to identify and troubleshoot errors in code, providing examples and emphasizing its importance in the debugging process.", 'duration': 232.046, 'highlights': ["The 'help 50' command, developed by the staff, assists in identifying and troubleshooting errors by analyzing error messages and providing advice. The chapter introduces the 'help 50' command, which was created by the staff to analyze error messages and offer advice on troubleshooting, enhancing the debugging process.", "Demonstration of the effectiveness of 'help 50' in providing specific advice for addressing errors, leading to progress in debugging. The transcript demonstrates the effectiveness of using the 'help 50' command to receive specific advice for addressing errors, leading to progress in the debugging process.", "Emphasizing the importance of using 'help 50' as the first instinct when encountering incomprehensible error messages, to aid in troubleshooting. The chapter emphasizes the importance of using the 'help 50' command as the first instinct when encountering incomprehensible error messages, highlighting its role in aiding troubleshooting efforts."]}, {'end': 1544.746, 'start': 1062.279, 'title': 'Debugging techniques in c programming', 'summary': "Discusses debugging techniques in c programming, emphasizing the use of printf for diagnostics, identifying and fixing logical errors, and adhering to coding style guidelines, while highlighting the tools 'help 50', 'printf', and 'style 50' as essential for debugging and code readability.", 'duration': 482.467, 'highlights': ['The chapter introduces debugging techniques in C programming, emphasizing the use of printf for diagnostics, identifying and fixing logical errors, and adhering to coding style guidelines.', "The speaker discusses the importance of using printf for diagnostic purposes, suggesting the printing of variable values and integers to understand the program's behavior.", "The chapter highlights the significance of adhering to coding style guidelines and using the tool 'style 50' to ensure code readability and conformity to the style guide.", "The speaker emphasizes the tools 'help 50', 'printf', and 'style 50' as essential for debugging and code readability, aiming to provide clear and understandable code for teaching fellows and colleagues."]}], 'duration': 1288.086, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I256660.jpg', 'highlights': ['The preprocessing step in the compilation process involves handling preprocessor directives demarcated by a hash, which are processed before everything else.', 'During the preprocessing step, Clang looks for included files on the hard drive and replaces specific lines of code, such as function declarations and definitions, from those files.', "Included files like CS50.h and standardio.h contain function declarations, such as get string and printf, which are essential for the program's functionality.", 'The chapter explains the C compilation process, including preprocessing, compiling, assembling, and linking, emphasizing the importance of each step.', 'It explains how the code is transformed from C to assembly language, then to machine code, and linked with other libraries to produce the final executable.', "The 'help 50' command, developed by the staff, assists in identifying and troubleshooting errors by analyzing error messages and providing advice.", "Demonstration of the effectiveness of 'help 50' in providing specific advice for addressing errors, leading to progress in debugging.", "Emphasizing the importance of using 'help 50' as the first instinct when encountering incomprehensible error messages, to aid in troubleshooting.", 'The chapter introduces debugging techniques in C programming, emphasizing the use of printf for diagnostics, identifying and fixing logical errors, and adhering to coding style guidelines.', "The speaker discusses the importance of using printf for diagnostic purposes, suggesting the printing of variable values and integers to understand the program's behavior.", "The chapter highlights the significance of adhering to coding style guidelines and using the tool 'style 50' to ensure code readability and conformity to the style guide.", "The speaker emphasizes the tools 'help 50', 'printf', and 'style 50' as essential for debugging and code readability, aiming to provide clear and understandable code for teaching fellows and colleagues."]}, {'end': 2418.552, 'segs': [{'end': 1633.705, 'src': 'embed', 'start': 1599.331, 'weight': 0, 'content': [{'end': 1601.353, 'text': 'But RAM is more ephemeral.', 'start': 1599.331, 'duration': 2.022}, {'end': 1603.954, 'text': 'RAM is powered only by electricity.', 'start': 1602.073, 'duration': 1.881}, {'end': 1606.914, 'text': "It's only used when the power is on or the battery is charged.", 'start': 1604.114, 'duration': 2.8}, {'end': 1612.416, 'text': "And it's where your files and programs live, effectively when you double click on them and open them.", 'start': 1607.174, 'duration': 5.242}, {'end': 1619.298, 'text': 'So when you double click on something like Microsoft Word, it is copied from your hard drive long term into this type of memory.', 'start': 1612.516, 'duration': 6.782}, {'end': 1626.92, 'text': "Because this type of memory, though smaller in capacity, you don't have as many bytes of it, But it is much, much, much, much faster.", 'start': 1619.618, 'duration': 7.302}, {'end': 1633.705, 'text': "Similarly, when you open a document or you go to a web page, the contents of the file you're seeing are stored in this type of hardware.", 'start': 1627.281, 'duration': 6.424}], 'summary': 'Ram is powered by electricity, faster but smaller in capacity, used when power is on or battery is charged.', 'duration': 34.374, 'max_score': 1599.331, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I1599331.jpg'}, {'end': 1769.894, 'src': 'embed', 'start': 1744.747, 'weight': 1, 'content': [{'end': 1752.116, 'text': 'But if we think about this grid, it turns out this is actually very valuable that we have chunks of memory bytes, if you will,', 'start': 1744.747, 'duration': 7.369}, {'end': 1754.359, 'text': 'that are back to back to back to back.', 'start': 1752.116, 'duration': 2.243}, {'end': 1756.602, 'text': "And in fact, there's a word for this technique.", 'start': 1754.419, 'duration': 2.183}, {'end': 1759.525, 'text': 'This is contiguous memory, back to back to back to back to back.', 'start': 1756.622, 'duration': 2.903}, {'end': 1762.989, 'text': 'And in general, in programming, this is referred to as an array.', 'start': 1759.745, 'duration': 3.244}, {'end': 1769.894, 'text': 'You might recall from Scratch, if you use this feature, it actually has things called lists, which are exactly that lists of values, lists of words,', 'start': 1763.77, 'duration': 6.124}], 'summary': 'Contiguous memory in programming is referred to as an array.', 'duration': 25.147, 'max_score': 1744.747, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I1744747.jpg'}, {'end': 1944.213, 'src': 'embed', 'start': 1917.964, 'weight': 2, 'content': [{'end': 1922.065, 'text': "And now I want to, it's not interesting to plot one score, so let's go ahead and do another.", 'start': 1917.964, 'duration': 4.101}, {'end': 1924.345, 'text': 'So int score 2, get int, get int.', 'start': 1922.145, 'duration': 2.2}, {'end': 1929.167, 'text': "And I'll ask the user for score 2, semicolon.", 'start': 1926.266, 'duration': 2.901}, {'end': 1934.969, 'text': "And then let's get one more, score 3, get int, call it score 3, semicolon.", 'start': 1929.207, 'duration': 5.762}, {'end': 1938.911, 'text': 'All right, so now let me go ahead and generate like a bar, like a bar chart of this.', 'start': 1935.31, 'duration': 3.601}, {'end': 1940.752, 'text': "I'm going to use what we'll call ASCII art.", 'start': 1938.931, 'duration': 1.821}, {'end': 1944.213, 'text': 'ASCII, of course, is just text, recall, very simple text in a computer.', 'start': 1941.052, 'duration': 3.161}], 'summary': 'Generating a bar chart using ascii art for multiple scores.', 'duration': 26.249, 'max_score': 1917.964, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I1917964.jpg'}, {'end': 2222.813, 'src': 'embed', 'start': 2195.397, 'weight': 3, 'content': [{'end': 2198.378, 'text': 'So loops are wonderful when you want to do something again and again and again.', 'start': 2195.397, 'duration': 2.981}, {'end': 2203.782, 'text': 'But the whole purpose of a function fundamentally is to factor out common functionality.', 'start': 2198.639, 'duration': 5.143}, {'end': 2205.743, 'text': 'And there might still be a loop in the solution.', 'start': 2203.802, 'duration': 1.941}, {'end': 2210.446, 'text': 'But the real fundamental problem of what I was doing a moment ago was I was copying and pasting functionality.', 'start': 2206.083, 'duration': 4.363}, {'end': 2214.789, 'text': "Shouldn't need to do that, because in both C and Scratch, we had the ability to make our own functions.", 'start': 2210.746, 'duration': 4.043}, {'end': 2216.13, 'text': "So let's do that.", 'start': 2215.189, 'duration': 0.941}, {'end': 2220.032, 'text': 'Let me undo my loop changes here, just to get us back to where we were a moment ago.', 'start': 2216.17, 'duration': 3.862}, {'end': 2222.813, 'text': 'And let me go ahead and instead clean this up a little bit.', 'start': 2220.412, 'duration': 2.401}], 'summary': 'Functions help eliminate repeated code. loops are useful for repetitive tasks.', 'duration': 27.416, 'max_score': 2195.397, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I2195397.jpg'}, {'end': 2427.616, 'src': 'embed', 'start': 2402.647, 'weight': 4, 'content': [{'end': 2407.749, 'text': "But I'm pushing the main part of my program, literally called main, farther and farther down.", 'start': 2402.647, 'duration': 5.102}, {'end': 2410.81, 'text': "And the whole point of reading code is to understand what it's doing.", 'start': 2407.829, 'duration': 2.981}, {'end': 2416.752, 'text': "So if I open this file and I have to scroll, scroll, scroll, scroll, scroll, just looking for the main function, that's just bad styles.", 'start': 2411.03, 'duration': 5.722}, {'end': 2418.552, 'text': "It's just kind of nice, and it's a good human convention.", 'start': 2416.812, 'duration': 1.74}, {'end': 2423.674, 'text': 'Put the main code, the main function, when green flag clicks equivalent, at the very top.', 'start': 2418.792, 'duration': 4.882}, {'end': 2425.895, 'text': 'So C does offer us a solution here.', 'start': 2423.934, 'duration': 1.961}, {'end': 2427.616, 'text': 'You just have to provide it with a little hint.', 'start': 2425.955, 'duration': 1.661}], 'summary': 'Place main code at the top for better readability and understanding.', 'duration': 24.969, 'max_score': 2402.647, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I2402647.jpg'}], 'start': 1544.746, 'title': 'Computer hardware, memory, and creating bar chart in c', 'summary': 'Covers computer hardware types like ram and hard drives, the significance of contiguous memory and arrays in programming, and creating a bar chart program in c using loops, functions, and arrays to avoid code redundancy.', 'chapters': [{'end': 1799.748, 'start': 1544.746, 'title': 'Computer hardware and memory', 'summary': 'Introduces the concept of computer hardware, focusing on the types of memory such as ram and hard drives, and explains the significance of contiguous memory and arrays in programming.', 'duration': 255.002, 'highlights': ['RAM vs. hard drives: RAM is ephemeral and faster, used when the power is on or the battery is charged, while hard drives store files permanently. RAM is powered only by electricity, used when power is on or battery is charged, and is much faster but smaller in capacity compared to hard drives.', 'Significance of contiguous memory: Contiguous memory, known as an array, enables efficient data storage and faster code execution. Contiguous memory, referred to as an array, allows back-to-back storage of data, enabling various possibilities in code design and execution speed.', "Types of memory and their role: CPUs, RAM, and hard drives play distinct roles in processing and storing data. CPUs are the brain's central processing unit, RAM is used when running programs or opening files, and hard drives store files permanently."]}, {'end': 2418.552, 'start': 1800.168, 'title': 'Creating bar chart in c', 'summary': 'Discusses creating a program in c that prompts a user for three scores, generates a simple bar chart using ascii art, and refactors the code to use a function and an array, highlighting the importance of loops and functions in avoiding code redundancy.', 'duration': 618.384, 'highlights': ['The chapter discusses creating a program in C that prompts a user for three scores and generates a simple bar chart using ASCII art. The program prompts the user for three scores, then uses ASCII art to create a visual bar chart, where a short bar represents a small number and a long bar represents a big number.', "The chapter emphasizes the importance of loops and functions in avoiding code redundancy. The chapter highlights the significance of using loops and functions to avoid code redundancy, demonstrating how to refactor the code to use a function called 'chart' and an array to improve design and reduce copy-pasting.", 'The importance of organizing code and avoiding unnecessary scrolling is discussed. The chapter emphasizes the importance of organizing code to avoid unnecessary scrolling and maintain good coding practices, highlighting the significance of placing the main function near the top of the program for better readability and understanding.']}], 'duration': 873.806, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I1544746.jpg', 'highlights': ['RAM vs. hard drives: RAM is ephemeral and faster, used when the power is on or the battery is charged, while hard drives store files permanently.', 'Contiguous memory, known as an array, enables efficient data storage and faster code execution.', 'The chapter discusses creating a program in C that prompts a user for three scores and generates a simple bar chart using ASCII art.', 'The chapter emphasizes the importance of loops and functions in avoiding code redundancy.', 'The importance of organizing code and avoiding unnecessary scrolling is discussed.']}, {'end': 3373.627, 'segs': [{'end': 2474.003, 'src': 'embed', 'start': 2444.102, 'weight': 0, 'content': [{'end': 2445.663, 'text': 'Give Clang enough information.', 'start': 2444.102, 'duration': 1.561}, {'end': 2450.928, 'text': 'so that it knows what arguments the function takes, what its return type is, and what its name is, semicolon.', 'start': 2446.303, 'duration': 4.625}, {'end': 2453.61, 'text': "And that's the so-called declaration.", 'start': 2451.208, 'duration': 2.402}, {'end': 2458.075, 'text': 'And then implement it with the curly braces and all the logic down below.', 'start': 2454.211, 'duration': 3.864}, {'end': 2459.416, 'text': "So let's go ahead and run this.", 'start': 2458.455, 'duration': 0.961}, {'end': 2462.359, 'text': "And if I scroll up here, we'll see.", 'start': 2460.177, 'duration': 2.182}, {'end': 2466.196, 'text': "Whoops We'll see make score 0.", 'start': 2462.519, 'duration': 3.677}, {'end': 2467.417, 'text': "All right, now we're on our way.", 'start': 2466.196, 'duration': 1.221}, {'end': 2468.978, 'text': 'Score 0, enter.', 'start': 2467.517, 'duration': 1.461}, {'end': 2469.777, 'text': 'Score 1 is 100, 50, 75.', 'start': 2469.078, 'duration': 0.699}, {'end': 2474.003, 'text': 'And now we seem to have some good functionality.', 'start': 2469.779, 'duration': 4.224}], 'summary': 'Declaring and implementing a function, running it, and achieving good functionality', 'duration': 29.901, 'max_score': 2444.102, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I2444102.jpg'}, {'end': 2530.389, 'src': 'embed', 'start': 2490.476, 'weight': 1, 'content': [{'end': 2491.998, 'text': 'give them all unique names.', 'start': 2490.476, 'duration': 1.522}, {'end': 2495.219, 'text': 'Because if I use the same variable for everything,', 'start': 2492.518, 'duration': 2.701}, {'end': 2501.042, 'text': "I couldn't collect all three variables at the top and then iterate over all three at the bottom if I only have one variable.", 'start': 2495.219, 'duration': 5.823}, {'end': 2504.264, 'text': "So I do need three variables, but this doesn't scale very well.", 'start': 2501.082, 'duration': 3.182}, {'end': 2511.128, 'text': "And who knows, if I want to take in five scores, 10 scores, or more scores, then I'm really copying and pasting excessively.", 'start': 2504.344, 'duration': 6.784}, {'end': 2513.711, 'text': 'So it turns out, indeed, the answer is an array.', 'start': 2511.508, 'duration': 2.203}, {'end': 2519.538, 'text': 'So an array, at the end of the day, is just a side effect of storing stuff in memory back to back to back to back.', 'start': 2514.071, 'duration': 5.467}, {'end': 2523.662, 'text': "But what's powerful about this reality of memory is the following.", 'start': 2519.558, 'duration': 4.104}, {'end': 2525.144, 'text': 'I can go ahead here.', 'start': 2524.083, 'duration': 1.061}, {'end': 2530.389, 'text': 'And in, say, a new and more improved version of this program, do this.', 'start': 2526.105, 'duration': 4.284}], 'summary': 'Using arrays for efficient storage and iteration in programming.', 'duration': 39.913, 'max_score': 2490.476, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I2490476.jpg'}, {'end': 2578.035, 'src': 'embed', 'start': 2552.886, 'weight': 3, 'content': [{'end': 2558.228, 'text': 'So the new syntax here is square brackets, and inside of which is the number of variables you want of that type.', 'start': 2552.886, 'duration': 5.342}, {'end': 2560.149, 'text': "And you don't have to give them unique names.", 'start': 2558.669, 'duration': 1.48}, {'end': 2562.33, 'text': 'You literally call them collectively scores.', 'start': 2560.229, 'duration': 2.101}, {'end': 2564.971, 'text': 'And in English, I deliberately chose a plural to connote as much.', 'start': 2562.39, 'duration': 2.581}, {'end': 2568.252, 'text': 'This is an array of values, not a single value.', 'start': 2565.011, 'duration': 3.241}, {'end': 2574.014, 'text': "What can I do next? Well, here's my for loop for int i gets 0, i is less than 3, i plus plus.", 'start': 2568.633, 'duration': 5.381}, {'end': 2576.835, 'text': "And now I've solved that earlier problem that was proposed.", 'start': 2574.374, 'duration': 2.461}, {'end': 2578.035, 'text': 'Well, just put it in a loop.', 'start': 2576.855, 'duration': 1.18}], 'summary': 'Introducing array syntax for multiple variables; using for loop to solve a proposed problem.', 'duration': 25.149, 'max_score': 2552.886, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I2552886.jpg'}, {'end': 2660.591, 'src': 'embed', 'start': 2628.521, 'weight': 4, 'content': [{'end': 2631.862, 'text': 'When i becomes 2 on the final iteration, it looks like this.', 'start': 2628.521, 'duration': 3.341}, {'end': 2637.023, 'text': "When i becomes 3, well, 3 is not less than 3, and so it doesn't execute again.", 'start': 2632.082, 'duration': 4.941}, {'end': 2644.446, 'text': 'So by using i inside of these square brackets, indexing into an array.', 'start': 2637.464, 'duration': 6.982}, {'end': 2650.347, 'text': 'To index into an array means go to a specific location, the so-called ith location, but you start counting at 0.', 'start': 2644.466, 'duration': 5.881}, {'end': 2660.591, 'text': "Just to make this more real, then if you go back to this picture of your computer's memory, this might therefore be bracket 0, bracket 1, bracket 2,", 'start': 2650.347, 'duration': 10.244}], 'summary': 'Demonstrating array indexing with i, starting from 0.', 'duration': 32.07, 'max_score': 2628.521, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I2628521.jpg'}, {'end': 2795.465, 'src': 'embed', 'start': 2766.664, 'weight': 5, 'content': [{'end': 2773.35, 'text': 'And now the onus is on me, the programmer, to remember to change the same damn value in multiple places, like bad, bad, bad design.', 'start': 2766.664, 'duration': 6.686}, {'end': 2775.051, 'text': "You're going to miss one of those values.", 'start': 2773.63, 'duration': 1.421}, {'end': 2776.332, 'text': "Your program's going to get more complex.", 'start': 2775.091, 'duration': 1.241}, {'end': 2778.874, 'text': "You're going to leave one at 3 and change the other to 5.", 'start': 2776.352, 'duration': 2.522}, {'end': 2781.015, 'text': 'And logical errors are eventually going to happen.', 'start': 2778.874, 'duration': 2.141}, {'end': 2784.718, 'text': "So how do we solve this? Function's not the solution here, because it's not functionality.", 'start': 2781.035, 'duration': 3.683}, {'end': 2785.598, 'text': "It's just a value.", 'start': 2784.758, 'duration': 0.84}, {'end': 2789, 'text': 'Well, we could use a variable, but a certain type of variable.', 'start': 2786.018, 'duration': 2.982}, {'end': 2795.465, 'text': 'These numbers here, 555 or 333, are what humans generally refer to as magic numbers.', 'start': 2789.341, 'duration': 6.124}], 'summary': 'Avoid using magic numbers to prevent errors and complexity in the program.', 'duration': 28.801, 'max_score': 2766.664, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I2766664.jpg'}, {'end': 2839.882, 'src': 'embed', 'start': 2800.008, 'weight': 6, 'content': [{'end': 2808.255, 'text': "But a better convention would be, often as a global variable, to do this, int, let's call it count equals 3.", 'start': 2800.008, 'duration': 8.247}, {'end': 2816.284, 'text': 'So declare a variable of type int, that is, the number of things you want, and then type that variable name all throughout your code,', 'start': 2808.255, 'duration': 8.029}, {'end': 2823.97, 'text': "so that later on, if you ever want to change this program, You change it in one place and you're done after recompiling the program.", 'start': 2816.284, 'duration': 7.686}, {'end': 2825.792, 'text': 'And actually, I should do a little better than this.', 'start': 2824.191, 'duration': 1.601}, {'end': 2830.935, 'text': "It turns out that if you know you have a variable, that you're never going to change, because it's not supposed to change.", 'start': 2825.852, 'duration': 5.083}, {'end': 2832.637, 'text': "It's supposed to be a constant value.", 'start': 2830.975, 'duration': 1.662}, {'end': 2839.882, 'text': 'C also has a special keyword called const, where before the data type, you say const int, and then the name, and then the value.', 'start': 2833.017, 'duration': 6.865}], 'summary': 'Use global variable or const for easy program modification and optimization.', 'duration': 39.874, 'max_score': 2800.008, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I2800008.jpg'}, {'end': 3132.381, 'src': 'embed', 'start': 3110.53, 'weight': 8, 'content': [{'end': 3119.015, 'text': "But again, the only point here is that you can indeed pass around arrays even as arguments, which we'll see why that's useful before long.", 'start': 3110.53, 'duration': 8.485}, {'end': 3123.93, 'text': 'Any questions? OK, so this was a lot.', 'start': 3119.975, 'duration': 3.955}, {'end': 3125.933, 'text': 'But we can do so much more still with arrays.', 'start': 3124.251, 'duration': 1.682}, {'end': 3127.315, 'text': "I think it's even more and more cool.", 'start': 3125.953, 'duration': 1.362}, {'end': 3132.381, 'text': "In fact, we'll see in just a bit how arrays have actually been with us since last week.", 'start': 3127.875, 'duration': 4.506}], 'summary': 'Arrays can be passed as arguments, offering more functionality and cool features.', 'duration': 21.851, 'max_score': 3110.53, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I3110530.jpg'}, {'end': 3174.149, 'src': 'embed', 'start': 3146.593, 'weight': 9, 'content': [{'end': 3154.957, 'text': 'And it turns out that last week, when we introduced strings, strings, sequences of characters, are literally just an array by another name.', 'start': 3146.593, 'duration': 8.364}, {'end': 3157.559, 'text': 'A string is an array of chars.', 'start': 3155.017, 'duration': 2.542}, {'end': 3159.42, 'text': 'And chars, of course, is another data type.', 'start': 3157.639, 'duration': 1.781}, {'end': 3165.483, 'text': 'Now, what are the actual implications of this, both in terms of representation, like how a computer is representing information,', 'start': 3159.7, 'duration': 5.783}, {'end': 3174.149, 'text': 'and then to fundamentally, programmatically, what can we do when we know all of our data is so back to back to back or so proximal to one another?', 'start': 3165.483, 'duration': 8.666}], 'summary': 'Strings are arrays of characters, with implications for representation and programming.', 'duration': 27.556, 'max_score': 3146.593, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I3146593.jpg'}], 'start': 2418.792, 'title': 'Arrays and functions in c', 'summary': 'Covers implementing functions, using arrays for memory management, introducing arrays, indexing, looping through arrays, and string manipulation, emphasizing the benefits of arrays and providing solutions for efficient programming. it highlights the necessity of proper function declaration and demonstrates the use of arrays for storing multiple values efficiently.', 'chapters': [{'end': 2530.389, 'start': 2418.792, 'title': 'Implementing functions and arrays', 'summary': 'Covers implementing functions and the use of arrays for better memory management and scalability in a program, highlighting the necessity of providing clang with proper function declaration and the benefits of using arrays for storing multiple values efficiently.', 'duration': 111.597, 'highlights': ['The necessity of providing Clang with proper function declaration including the arguments, return type, and name is emphasized for implementing functions effectively and ensuring their correct usage.', 'The limitations of using individual variables for storing multiple values are highlighted, demonstrating the inefficiency and lack of scalability when dealing with a large number of values in a program.', 'The benefits of using arrays for efficiently storing multiple values are explained, emphasizing the improved memory management and scalability they offer compared to using individual variables.']}, {'end': 2974.236, 'start': 2530.549, 'title': 'Arrays and loops in c', 'summary': 'Covers the use of arrays and loops in c, introducing the concept of arrays, indexing, and looping through arrays, emphasizing the benefits of using arrays and the potential issues with redundant code and the solution using global constants.', 'duration': 443.687, 'highlights': ['The chapter introduces the concept of arrays in C, demonstrating the use of square brackets to declare multiple variables of the same type, offering the example of creating an array of scores with three elements, and highlighting the benefits of using arrays to store multiple values efficiently. array of scores with three elements', 'The chapter explains the use of loops to iterate through arrays, showcasing a for loop to access and manipulate array elements, and highlighting the ability to use index variables to access specific elements within the array. demonstrates the use of for loop for accessing array elements', "The chapter addresses the issue of redundant code by identifying the repetition of the number '3' in multiple places, emphasizing the potential for logical errors and complexity in the program when values are hardcoded in various locations. repetition of the number '3' in multiple places", "The chapter proposes the use of global constants to address the issue of redundant code, explaining the use of a variable as a global constant to store the value '3' and highlighting the benefits of changing the value in one place, ensuring consistency throughout the program. use of global constants to store the value '3'", 'The chapter introduces the concept of const keyword in C to define constant values, emphasizing the role of the compiler in enforcing the immutability of the variable and promoting the use of const to prevent inadvertent changes to the constant value. introduces the const keyword in C to define constant values']}, {'end': 3373.627, 'start': 2974.816, 'title': 'Array functions and strings', 'summary': 'Discusses the use of arrays and their functions, including iterating over arrays, passing arrays as arguments, and indexing strings as arrays. it also introduces the concept of strings as arrays of characters, and demonstrates the use of the string length function to iterate over characters in a string.', 'duration': 398.811, 'highlights': ['The chapter discusses the use of arrays and their functions, including iterating over arrays, passing arrays as arguments, and indexing strings as arrays. The chapter covers the functionality of arrays, such as iterating over arrays, passing arrays as arguments, and indexing strings as arrays.', 'It introduces the concept of strings as arrays of characters and demonstrates the use of the string length function to iterate over characters in a string. The concept of strings as arrays of characters is introduced, and the usage of the string length function to iterate over characters in a string is demonstrated.']}], 'duration': 954.835, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I2418792.jpg', 'highlights': ['The necessity of providing Clang with proper function declaration including the arguments, return type, and name is emphasized for implementing functions effectively and ensuring their correct usage.', 'The benefits of using arrays for efficiently storing multiple values are explained, emphasizing the improved memory management and scalability they offer compared to using individual variables.', 'The limitations of using individual variables for storing multiple values are highlighted, demonstrating the inefficiency and lack of scalability when dealing with a large number of values in a program.', 'The chapter introduces the concept of arrays in C, demonstrating the use of square brackets to declare multiple variables of the same type, offering the example of creating an array of scores with three elements, and highlighting the benefits of using arrays to store multiple values efficiently.', 'The chapter explains the use of loops to iterate through arrays, showcasing a for loop to access and manipulate array elements, and highlighting the ability to use index variables to access specific elements within the array.', "The chapter addresses the issue of redundant code by identifying the repetition of the number '3' in multiple places, emphasizing the potential for logical errors and complexity in the program when values are hardcoded in various locations.", "The chapter proposes the use of global constants to address the issue of redundant code, explaining the use of a variable as a global constant to store the value '3' and highlighting the benefits of changing the value in one place, ensuring consistency throughout the program.", 'The chapter introduces the concept of const keyword in C to define constant values, emphasizing the role of the compiler in enforcing the immutability of the variable and promoting the use of const to prevent inadvertent changes to the constant value.', 'The chapter discusses the use of arrays and their functions, including iterating over arrays, passing arrays as arguments, and indexing strings as arrays.', 'It introduces the concept of strings as arrays of characters and demonstrates the use of the string length function to iterate over characters in a string.']}, {'end': 4150.974, 'segs': [{'end': 3426.021, 'src': 'embed', 'start': 3393.262, 'weight': 6, 'content': [{'end': 3395.084, 'text': "If we're defining string in CS50, are we redefining it in string? No.", 'start': 3393.262, 'duration': 1.822}, {'end': 3399.33, 'text': "So string, even though it's named string.h, doesn't actually define something called a string.", 'start': 3395.124, 'duration': 4.206}, {'end': 3401.513, 'text': 'It just has string-related functions.', 'start': 3399.731, 'duration': 1.782}, {'end': 3403.916, 'text': 'More on that soon.', 'start': 3403.215, 'duration': 0.701}, {'end': 3408.934, 'text': 'Yeah? Ah, really good question.', 'start': 3403.956, 'duration': 4.978}, {'end': 3413.256, 'text': 'Could you edit the individual values? So short answer, yes.', 'start': 3408.954, 'duration': 4.302}, {'end': 3415.357, 'text': 'We could absolutely change values.', 'start': 3413.436, 'duration': 1.921}, {'end': 3417.518, 'text': "And we'll soon do that in another context.", 'start': 3415.417, 'duration': 2.101}, {'end': 3420.359, 'text': 'Other questions? All right.', 'start': 3418.398, 'duration': 1.961}, {'end': 3426.021, 'text': "So turns out this is correct if my goal is to print out all of the characters in Zamyla's name.", 'start': 3420.599, 'duration': 5.422}], 'summary': 'In cs50, string.h does not define a string, only string-related functions. values can be edited.', 'duration': 32.759, 'max_score': 3393.262, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I3393262.jpg'}, {'end': 3465.347, 'src': 'embed', 'start': 3437.326, 'weight': 0, 'content': [{'end': 3441.309, 'text': "Up until today, we've introduced the notion of correctness in both Scratch and in C last week.", 'start': 3437.326, 'duration': 3.983}, {'end': 3444.612, 'text': "But now we're introducing these other axes of quality of code,", 'start': 3441.55, 'duration': 3.062}, {'end': 3449.337, 'text': 'like design how well designed it is and how pretty does it look in the context of style.', 'start': 3444.612, 'duration': 4.725}, {'end': 3455.142, 'text': 'So expectations are here on out meant to be aligned with those characteristics, but not in the past.', 'start': 3449.377, 'duration': 5.765}, {'end': 3457.803, 'text': "So there's a slight inefficiency here.", 'start': 3455.442, 'duration': 2.361}, {'end': 3465.347, 'text': 'So, on the first iteration of this loop, I first initialize i to 0, and then I check if i is less than the length of the string,', 'start': 3458.083, 'duration': 7.264}], 'summary': 'Introducing design and style as new axes of code quality.', 'duration': 28.021, 'max_score': 3437.326, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I3437326.jpg'}, {'end': 3509.116, 'src': 'embed', 'start': 3479.113, 'weight': 1, 'content': [{'end': 3482.635, 'text': "We looped through loops last week, and you've used them perhaps by now in problems.", 'start': 3479.113, 'duration': 3.522}, {'end': 3495.675, 'text': 'What question am I redundantly asking seemingly unnecessarily? I have to check a condition again and again because i is getting incremented.', 'start': 3483.88, 'duration': 11.795}, {'end': 3501.563, 'text': "But there's another question that I don't need to keep asking again just to get the same answer.", 'start': 3495.695, 'duration': 5.868}, {'end': 3509.116, 'text': "Yeah, there's this function call in my loop of strlen s, which is fine.", 'start': 3503.991, 'duration': 5.125}], 'summary': 'Looped through loops, used in problems, checking condition, and function call in loop of strlen s.', 'duration': 30.003, 'max_score': 3479.113, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I3479113.jpg'}, {'end': 3591.351, 'src': 'embed', 'start': 3563.368, 'weight': 2, 'content': [{'end': 3568.229, 'text': "If you're using a loop, a secret feature of loops is that you can have commas after declaring variables.", 'start': 3563.368, 'duration': 4.861}, {'end': 3575.672, 'text': 'And you can actually do this and make this even more elegant, if you will, or more confusing looking, depending on your perspective.', 'start': 3568.55, 'duration': 7.122}, {'end': 3580.934, 'text': "But this now does the same thing, but declares n inside of the loop, just like I'm declaring i.", 'start': 3575.992, 'duration': 4.942}, {'end': 3581.914, 'text': "And it's just a little tighter.", 'start': 3580.934, 'duration': 0.98}, {'end': 3584.195, 'text': "It's one fewer lines of code.", 'start': 3581.974, 'duration': 2.221}, {'end': 3591.351, 'text': 'Any questions, then? Good question.', 'start': 3585.356, 'duration': 5.995}], 'summary': 'Using commas after declaring variables in loops can make code more elegant or confusing, but it results in one fewer line of code.', 'duration': 27.983, 'max_score': 3563.368, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I3563368.jpg'}, {'end': 3810.222, 'src': 'embed', 'start': 3781.798, 'weight': 4, 'content': [{'end': 3783.581, 'text': 'So for instance, let me go ahead and do this.', 'start': 3781.798, 'duration': 1.783}, {'end': 3787.606, 'text': 'Let me go ahead and create a program called called strlen itself.', 'start': 3783.661, 'duration': 3.945}, {'end': 3790.548, 'text': 'So this is not a function, but a program called stringlength.c.', 'start': 3787.666, 'duration': 2.882}, {'end': 3793.471, 'text': 'Let me go ahead and include the CS50 library at the top.', 'start': 3790.889, 'duration': 2.582}, {'end': 3796.173, 'text': 'Let me go ahead and include standardio.h.', 'start': 3793.791, 'duration': 2.382}, {'end': 3798.155, 'text': 'Let me go ahead and type out int main void.', 'start': 3796.234, 'duration': 1.921}, {'end': 3800.177, 'text': 'So all this is same as always.', 'start': 3798.175, 'duration': 2.002}, {'end': 3805.541, 'text': 'And then let me go ahead and prompt the user for, say his or her name, like so.', 'start': 3800.618, 'duration': 4.923}, {'end': 3810.222, 'text': "And then, you know what? Let me actually this time not just print their name out, because we've done that ad nauseum.", 'start': 3806.101, 'duration': 4.121}], 'summary': 'Creating a program to prompt user for name, using cs50 library.', 'duration': 28.424, 'max_score': 3781.798, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I3781798.jpg'}, {'end': 3957.788, 'src': 'embed', 'start': 3934.14, 'weight': 3, 'content': [{'end': 3942.082, 'text': 'And we get to z, a, m, y, l, a, then all 0s, the so-called null character, or backslash 0.', 'start': 3934.14, 'duration': 7.942}, {'end': 3944.203, 'text': 'That, of course, does equal backslash 0.', 'start': 3942.082, 'duration': 2.121}, {'end': 3951.605, 'text': 'So the loop stops, thereby leaving the total count or value of n at what it previously was, which was 6.', 'start': 3944.203, 'duration': 7.402}, {'end': 3952.165, 'text': "So that's it.", 'start': 3951.605, 'duration': 0.56}, {'end': 3957.788, 'text': 'All underneath the hood, all we have is memory laid out like this, top to bottom, left to right.', 'start': 3952.185, 'duration': 5.603}], 'summary': 'The loop stops at null character, leaving the total count at 6.', 'duration': 23.648, 'max_score': 3934.14, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I3934140.jpg'}, {'end': 4139.067, 'src': 'embed', 'start': 4111.095, 'weight': 5, 'content': [{'end': 4115.077, 'text': 'And down here I can literally just print the same thing twice,', 'start': 4111.095, 'duration': 3.982}, {'end': 4121.679, 'text': 'but tell printf to print the first in the context of a character and the second in the context of an int,', 'start': 4115.077, 'duration': 6.602}, {'end': 4124.08, 'text': 'just treating the exact same bits differently.', 'start': 4121.679, 'duration': 2.401}, {'end': 4126.321, 'text': "That's implicit casting.", 'start': 4124.841, 'duration': 1.48}, {'end': 4133.524, 'text': 'And it just demonstrates what we did in week 0, when we claimed that letters are numbers and numbers can also be colors,', 'start': 4126.902, 'duration': 6.622}, {'end': 4134.984, 'text': 'and colors can be images and so forth.', 'start': 4133.524, 'duration': 1.46}, {'end': 4137.026, 'text': 'Is this a question? It would have been useful for credit.', 'start': 4135.325, 'duration': 1.701}, {'end': 4139.067, 'text': 'Also, yes, it all comes back to credit.', 'start': 4137.526, 'duration': 1.541}], 'summary': 'Demonstrating implicit casting in programming and the relationship between letters, numbers, and colors.', 'duration': 27.972, 'max_score': 4111.095, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I4111095.jpg'}], 'start': 3373.627, 'title': 'String functions, design, optimizing loops, and memory usage', 'summary': 'Discusses the definition of a string in cs50, editing individual values, and introducing the axes of quality of code, like design and style. it also covers optimizing loops and memory usage, demonstrating the benefits of caching and efficient loop design while exploring the underlying implementation of string length and ascii conversion.', 'chapters': [{'end': 3457.803, 'start': 3373.627, 'title': 'Cs50: string functions and design', 'summary': 'Discusses the definition of a string in cs50, editing individual values, and introducing the axes of quality of code, like design and style. it emphasizes the importance of good design and aligning expectations with the characteristics of the code.', 'duration': 84.176, 'highlights': ['The chapter clarifies that defining a string in CS50 does not actually define something called a string, but it includes string-related functions.', 'The discussion emphasizes the ability to edit individual values in the context of strings.', 'The chapter introduces the importance of good design and aligning expectations with the characteristics of the code, including style and efficiency.']}, {'end': 4150.974, 'start': 3458.083, 'title': 'Optimizing loops and memory usage', 'summary': 'Discusses optimizing loops and memory usage, demonstrating the benefits of caching and efficient loop design while exploring the underlying implementation of string length and ascii conversion.', 'duration': 692.891, 'highlights': ['Explaining the benefits of caching the answer of a function call by using a variable instead of repeatedly calling the function. By caching the length of the string in a variable, it reduces the need to repeatedly call the strlen function, improving performance and efficiency.', 'Demonstrating the optimization of loops by declaring variables within the loop and using commas after declaring variables. The feature of declaring variables within loops and using commas after variable declarations can lead to more elegant and concise code, reducing the number of lines and improving readability.', 'Exploring the underlying memory layout and the use of null characters to represent the end of strings in memory. The discussion delves into the concept of strings in memory, emphasizing the use of null characters to signify the end of strings and the underlying memory layout of characters.', 'Demonstrating the manual implementation of the strlen function by iterating through characters until the null character is encountered. The manual implementation of the strlen function is illustrated, showcasing the process of iterating through characters until the null character is found to determine the length of the string.', 'Exploring ASCII conversion and the ability to manipulate individual characters by casting them to integers. The chapter introduces the concept of ASCII conversion and demonstrates the manipulation of characters by casting them to integers, allowing for the interpretation of characters as numerical values.']}], 'duration': 777.347, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I3373627.jpg', 'highlights': ['The chapter introduces the importance of good design and aligning expectations with the characteristics of the code, including style and efficiency.', 'Explaining the benefits of caching the answer of a function call by using a variable instead of repeatedly calling the function. By caching the length of the string in a variable, it reduces the need to repeatedly call the strlen function, improving performance and efficiency.', 'Demonstrating the optimization of loops by declaring variables within the loop and using commas after declaring variables. The feature of declaring variables within loops and using commas after variable declarations can lead to more elegant and concise code, reducing the number of lines and improving readability.', 'Exploring the underlying memory layout and the use of null characters to represent the end of strings in memory. The discussion delves into the concept of strings in memory, emphasizing the use of null characters to signify the end of strings and the underlying memory layout of characters.', 'Demonstrating the manual implementation of the strlen function by iterating through characters until the null character is encountered. The manual implementation of the strlen function is illustrated, showcasing the process of iterating through characters until the null character is found to determine the length of the string.', 'Exploring ASCII conversion and the ability to manipulate individual characters by casting them to integers. The chapter introduces the concept of ASCII conversion and demonstrates the manipulation of characters by casting them to integers, allowing for the interpretation of characters as numerical values.', 'The chapter clarifies that defining a string in CS50 does not actually define something called a string, but it includes string-related functions.', 'The discussion emphasizes the ability to edit individual values in the context of strings.']}, {'end': 5098.31, 'segs': [{'end': 4188.143, 'src': 'embed', 'start': 4164.381, 'weight': 0, 'content': [{'end': 4173.149, 'text': 'And you know that these characters have numbers representing them, and capital A is 65, and lowercase a is 97,, apparently, and so forth.', 'start': 4164.381, 'duration': 8.768}, {'end': 4175.072, 'text': 'We can leverage these patterns.', 'start': 4173.711, 'duration': 1.361}, {'end': 4182.919, 'text': 'If I go ahead and open up this other example here called capitalize0, notice what this program is going to do for me first by running it.', 'start': 4175.453, 'duration': 7.466}, {'end': 4184.56, 'text': 'Make capitalize0.', 'start': 4183.54, 'duration': 1.02}, {'end': 4188.143, 'text': 'Dot slash capitalize 0.', 'start': 4185.862, 'duration': 2.281}], 'summary': 'Characters represented by numbers, a=65, a=97. leveraging patterns in program.', 'duration': 23.762, 'max_score': 4164.381, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I4164381.jpg'}, {'end': 4435.884, 'src': 'embed', 'start': 4410.156, 'weight': 1, 'content': [{'end': 4414.498, 'text': 'ToUpper is another feature, right? This math, like my god, I just want to uppercase a letter.', 'start': 4410.156, 'duration': 4.342}, {'end': 4417.979, 'text': "I don't want to really keep thinking about how far apart uppercase letters are from lowercase.", 'start': 4414.518, 'duration': 3.461}, {'end': 4425.281, 'text': "Turns out that in the ctype library there's another function called toUpper that literally does the exact same thing. in the previous program we wrote", 'start': 4418.359, 'duration': 6.922}, {'end': 4427.422, 'text': 'And so that too is OK.', 'start': 4425.841, 'duration': 1.581}, {'end': 4430.843, 'text': 'But you know what? This feels a little verbose.', 'start': 4428.382, 'duration': 2.461}, {'end': 4433.924, 'text': 'It would be nice if I could really tighten this program up.', 'start': 4431.343, 'duration': 2.581}, {'end': 4435.884, 'text': 'So how does toUpper work?', 'start': 4434.004, 'duration': 1.88}], 'summary': 'Introducing the toupper feature for uppercase conversion in the ctype library.', 'duration': 25.728, 'max_score': 4410.156, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I4410156.jpg'}, {'end': 4875.323, 'src': 'embed', 'start': 4840.657, 'weight': 2, 'content': [{'end': 4842.738, 'text': 'argc tells you how many words were typed at the prompt.', 'start': 4840.657, 'duration': 2.081}, {'end': 4849.162, 'text': 'So if the human typed two words, I presume the first word is the name of the program, dot slash argv 0.', 'start': 4843.018, 'duration': 6.144}, {'end': 4853.444, 'text': 'The second word is presumably my name, if he or she is actually providing their name at the prompt.', 'start': 4849.162, 'duration': 4.282}, {'end': 4859.147, 'text': "And so I print out argv bracket 1, not 0, because that's the name of the program, but argv bracket 1.", 'start': 4853.524, 'duration': 5.623}, {'end': 4867.032, 'text': "Else, down here, if the human doesn't provide just Zamyla or just David or just one word more generally, I just print the default, hello world.", 'start': 4859.147, 'duration': 7.885}, {'end': 4875.323, 'text': "But what's neat about this now is notice that, argv is an array of strings.", 'start': 4867.792, 'duration': 7.531}], 'summary': 'Using argc and argv to process user input in c, handling different cases to print specific output.', 'duration': 34.666, 'max_score': 4840.657, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I4840657.jpg'}], 'start': 4151.014, 'title': 'Automatic capitalization and character manipulation in c', 'summary': "Discusses automatic capitalization in text editors, covering google docs and microsoft word's character encoding usage. it also explores character manipulation in c, converting lowercase letters to uppercase, and working with command line arguments to accept words and numbers, showcasing the power of utilizing arrays in c programming.", 'chapters': [{'end': 4201.972, 'start': 4151.014, 'title': 'Automatic capitalization in text editors', 'summary': 'Discusses how text editors like google docs and microsoft word use character encoding to automatically capitalize words, leveraging the patterns of character numbers. it also demonstrates a program that capitalizes all letters in a name, emphasizing the concept of automatic capitalization.', 'duration': 50.958, 'highlights': ['The process of automatic capitalization in text editors is based on leveraging the patterns of character numbers, where capital A is 65 and lowercase a is 97, among others.', 'The demonstration of a program capitalizing all letters in a name illustrates the concept of automatic capitalization, offering practical insight into the process.', 'The chapter explains how modern text editors and phones are capable of automatic capitalization, showcasing the widespread use of this feature in technology.']}, {'end': 4492.081, 'start': 4203.638, 'title': 'Working with characters in c', 'summary': 'Explores a program in c that manipulates characters in a string, converting lowercase letters to uppercase using math and functions from ctype.h library, providing insights into the use of functions and abstractions in programming.', 'duration': 288.443, 'highlights': ['The program manipulates characters in a string, converting lowercase letters to uppercase using math and functions from ctype.h library. The program showcases the efficient manipulation of characters in a string, demonstrating the conversion of lowercase letters to uppercase using mathematical operations and predefined functions from the ctype.h library.', 'Insights into the use of functions and abstractions in programming. The chapter provides insights into the use of prewritten functions and abstractions, emphasizing the benefits of leveraging existing functions such as islower, isupper, and toUpper from the ctype.h library for character manipulation.', 'Exploration of the use of the ctype.h library and the functions it offers for character manipulation. The chapter delves into the exploration of the ctype.h library, highlighting the availability of functions like islower, isupper, and toUpper for character manipulation, providing a more efficient and concise approach to working with characters in C.']}, {'end': 5098.31, 'start': 4492.121, 'title': 'Working with command line arguments', 'summary': 'Discusses the usage of command line arguments in c programming, highlighting how to use the argc and argv parameters to accept words and numbers when running a program, resulting in more compact and efficient code. it also showcases how to access and manipulate the array of arguments and characters within the arguments, demonstrating the power of utilizing arrays in c programming.', 'duration': 606.189, 'highlights': ['The chapter discusses the usage of command line arguments in C programming, highlighting how to use the argc and argv parameters to accept words and numbers when running a program. argc and argv parameters enable the program to accept words and numbers when run, resulting in more user-friendly and versatile programs.', 'It also showcases how to access and manipulate the array of arguments and characters within the arguments, demonstrating the power of utilizing arrays in C programming. Demonstrates the ability to access and manipulate the array of arguments and characters within them, showcasing the versatility and power of utilizing arrays in C programming.', 'The chapter emphasizes how understanding command line arguments can lead to more compact and efficient code, resulting in better-designed programs. Understanding command line arguments leads to more compact and efficient code, resulting in better-designed programs.']}], 'duration': 947.296, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I4151014.jpg', 'highlights': ['The process of automatic capitalization in text editors is based on leveraging the patterns of character numbers, where capital A is 65 and lowercase a is 97, among others.', 'The program manipulates characters in a string, converting lowercase letters to uppercase using math and functions from ctype.h library.', 'The chapter discusses the usage of command line arguments in C programming, highlighting how to use the argc and argv parameters to accept words and numbers when running a program.']}, {'end': 5597.946, 'segs': [{'end': 5124.006, 'src': 'embed', 'start': 5098.35, 'weight': 4, 'content': [{'end': 5104.993, 'text': 'But suppose the problem that you want to solve is to actually pass a secret message in class or send someone a secret for whatever reason.', 'start': 5098.35, 'duration': 6.643}, {'end': 5109.496, 'text': 'Well, the input to that problem is generally called plaintext, a message you want to send to that other person.', 'start': 5105.033, 'duration': 4.463}, {'end': 5112.257, 'text': 'You ideally want ciphertext to emerge from it.', 'start': 5109.776, 'duration': 2.481}, {'end': 5118.422, 'text': 'which is enciphered and scrambled, somehow encrypted information, so that anyone in the room, like the teacher,', 'start': 5112.877, 'duration': 5.545}, {'end': 5124.006, 'text': "can't just grab the note and read what you're sending to your secret crusher all across the room or in any other context as well.", 'start': 5118.422, 'duration': 5.584}], 'summary': 'Encrypt plaintext to ciphertext for secure message transmission.', 'duration': 25.656, 'max_score': 5098.35, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I5098350.jpg'}, {'end': 5207.272, 'src': 'embed', 'start': 5176.617, 'weight': 1, 'content': [{'end': 5178.098, 'text': 'Well, you can be a little more sophisticated.', 'start': 5176.617, 'duration': 1.481}, {'end': 5186.228, 'text': 'And this is back actually a photograph from World War I of a message that was sent from Germany to Mexico that was encoded in very similar way.', 'start': 5178.598, 'duration': 7.63}, {'end': 5187.249, 'text': "It wasn't using ASCII.", 'start': 5186.248, 'duration': 1.001}, {'end': 5190.573, 'text': 'The numbers, as you can perhaps glean from the photo, are actually much larger.', 'start': 5187.269, 'duration': 3.304}, {'end': 5193.978, 'text': 'But in this system, in a militaristic context, there was a code book.', 'start': 5190.914, 'duration': 3.064}, {'end': 5200.204, 'text': 'So similar in spirit to ASCII, where you have a column of numbers and a column of letters to which they correspond.', 'start': 5194.318, 'duration': 5.886}, {'end': 5207.272, 'text': 'a code book more generally has numbers and then maybe even letters or whole words that they correspond to, sometimes thousands of them,', 'start': 5200.204, 'duration': 7.068}], 'summary': 'World war i message encoded in a sophisticated manner using a code book, with thousands of numbers and letters.', 'duration': 30.655, 'max_score': 5176.617, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I5176617.jpg'}, {'end': 5235.031, 'src': 'embed', 'start': 5210.715, 'weight': 2, 'content': [{'end': 5217.08, 'text': 'And so long as only in this context the Germans and the recipients, the Mexicans, had access to that same book.', 'start': 5210.715, 'duration': 6.365}, {'end': 5221.483, 'text': 'only they could encrypt and decrypt, or rather encode and decode information.', 'start': 5217.08, 'duration': 4.403}, {'end': 5228.769, 'text': 'Of course, in this very specific context and you can read more about this in historical texts this was intercepted, this message seemingly innocuous,', 'start': 5221.543, 'duration': 7.226}, {'end': 5231.17, 'text': 'though definitely suspicious, looking with all these numbers.', 'start': 5228.769, 'duration': 2.401}, {'end': 5235.031, 'text': 'So therefore, not innocuous.', 'start': 5232.27, 'duration': 2.761}], 'summary': 'Germans and mexicans encrypted messages using a shared book, intercepted message contained suspicious numbers.', 'duration': 24.316, 'max_score': 5210.715, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I5210715.jpg'}, {'end': 5344.347, 'src': 'embed', 'start': 5304.105, 'weight': 0, 'content': [{'end': 5310.308, 'text': 'Because if the revolutionaries and the American Revolution kind of decided secretly among themselves literally that.', 'start': 5304.105, 'duration': 6.203}, {'end': 5314.951, 'text': 'We will put up one light at the top of a church if the British are coming by land,', 'start': 5310.548, 'duration': 4.403}, {'end': 5318.133, 'text': 'and we will instead use two if the British are instead coming by sea.', 'start': 5314.951, 'duration': 3.182}, {'end': 5319.254, 'text': 'Like, that is a code.', 'start': 5318.173, 'duration': 1.081}, {'end': 5321.736, 'text': 'And you could write it down in a book, and thus you have a code book.', 'start': 5319.334, 'duration': 2.402}, {'end': 5325.998, 'text': "But of course, as soon as someone figures out that pattern, it's compromised.", 'start': 5322.156, 'duration': 3.842}, {'end': 5331.701, 'text': 'And so codebooks tend not to be the most robust mechanisms for encoding information.', 'start': 5326.138, 'duration': 5.563}, {'end': 5335.203, 'text': "Instead, it's better to use something more algorithmic.", 'start': 5332.081, 'duration': 3.122}, {'end': 5336.663, 'text': 'And wonderfully, in computer science.', 'start': 5335.243, 'duration': 1.42}, {'end': 5339.805, 'text': 'is this black box, do we keep saying, the home of algorithms?', 'start': 5336.663, 'duration': 3.142}, {'end': 5344.347, 'text': 'And in general, encryption is a problem with inputs and outputs.', 'start': 5340.365, 'duration': 3.982}], 'summary': 'Revolutionaries used a signaling code to warn about british movements, emphasizing the importance of algorithmic encryption in computer science.', 'duration': 40.242, 'max_score': 5304.105, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I5304105.jpg'}, {'end': 5597.946, 'src': 'embed', 'start': 5573.007, 'weight': 5, 'content': [{'end': 5578.532, 'text': 'but hopefully not just using a key of 1, maybe 2 or 13 or 25 or something larger.', 'start': 5573.007, 'duration': 5.525}, {'end': 5584.957, 'text': "But this is an example of a substitution cipher or a rotational cipher, where everything's kind of rotating.", 'start': 5578.872, 'duration': 6.085}, {'end': 5590.502, 'text': 'A is becoming B, B is becoming C, or you can kind of rotate it even further than that.', 'start': 5585.118, 'duration': 5.384}, {'end': 5597.946, 'text': "Well, let's take a look at one last example here of just one other final primitive of a feature today,", 'start': 5591.423, 'duration': 6.523}], 'summary': 'Example of rotational cipher with different keys, demonstrating letter rotation.', 'duration': 24.939, 'max_score': 5573.007, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I5573007.jpg'}], 'start': 5098.35, 'title': 'Cryptography and encryption techniques', 'summary': 'Delves into the significance of cryptography in securing secret messages, emphasizing the limitations of simple encoding methods like ascii. it also discusses historical code techniques and encryption concepts, featuring examples from world war i and the american revolution.', 'chapters': [{'end': 5249.658, 'start': 5098.35, 'title': 'Cryptography and secret messages', 'summary': 'Discusses the importance of cryptography in securing secret messages, highlighting the inadequacy of simple encoding methods like ascii and the need for sophisticated encryption techniques, illustrated through a historical example from world war i.', 'duration': 151.308, 'highlights': ['The importance of secure communication through cryptography is demonstrated by the inadequacy of simple encoding methods like ASCII, which can be easily decoded by anyone familiar with the system.', 'The significance of using sophisticated encryption techniques is emphasized through a historical example from World War I, where a code book was utilized to securely encrypt and decrypt messages, highlighting the importance of a unique and secure system.', 'The example from World War I illustrates the interception of a seemingly innocuous message, encrypted using a code book, and the subsequent successful decryption through cryptanalysis, showcasing the significance of robust encryption methods in safeguarding sensitive information.']}, {'end': 5597.946, 'start': 5250.198, 'title': 'Code techniques and encryption', 'summary': 'Explores historical code techniques like the one if by land and two if by sea code used during the american revolution, and the concept of encryption using a secret key, highlighting the use of algorithms and the caesar cipher.', 'duration': 347.748, 'highlights': ['The one if by land and two if by sea code were an example of a one-time code used during the American Revolution. This historical code technique was used by the revolutionaries to secretly communicate about the British movements and was an example of a one-time code.', 'Encryption involves using a secret key or a number to encode a message, making it more private and secure. The concept of using a secret key in encryption to encode messages is highlighted, emphasizing the importance of secrecy for secure communication.', 'The Caesar cipher was used as an example of a substitution cipher, where letters are rotated by a certain number, demonstrating a primitive code technique. The explanation of the Caesar cipher as a primitive substitution cipher and its usage as a code technique, showcasing the historical significance of encryption methods.']}], 'duration': 499.596, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I5098350.jpg', 'highlights': ['The importance of secure communication through cryptography is demonstrated by the inadequacy of simple encoding methods like ASCII, which can be easily decoded by anyone familiar with the system.', 'The significance of using sophisticated encryption techniques is emphasized through a historical example from World War I, where a code book was utilized to securely encrypt and decrypt messages, highlighting the importance of a unique and secure system.', 'The example from World War I illustrates the interception of a seemingly innocuous message, encrypted using a code book, and the subsequent successful decryption through cryptanalysis, showcasing the significance of robust encryption methods in safeguarding sensitive information.', 'The one if by land and two if by sea code were an example of a one-time code used during the American Revolution. This historical code technique was used by the revolutionaries to secretly communicate about the British movements and was an example of a one-time code.', 'Encryption involves using a secret key or a number to encode a message, making it more private and secure. The concept of using a secret key in encryption to encode messages is highlighted, emphasizing the importance of secrecy for secure communication.', 'The Caesar cipher was used as an example of a substitution cipher, where letters are rotated by a certain number, demonstrating a primitive code technique. The explanation of the Caesar cipher as a primitive substitution cipher and its usage as a code technique, showcasing the historical significance of encryption methods.']}, {'end': 6738.712, 'segs': [{'end': 5865.261, 'src': 'embed', 'start': 5841.312, 'weight': 1, 'content': [{'end': 5849.035, 'text': 'So it turns out that an array you can kind of think of it as a series of lockers a series of lockers that might look like this,', 'start': 5841.312, 'duration': 7.723}, {'end': 5852.756, 'text': 'inside of which are values, strings or numbers, or chars, or whatnot.', 'start': 5849.035, 'duration': 3.721}, {'end': 5858.918, 'text': 'But the lockers is an apt metaphor because a computer, unlike us humans, can only see and do one thing at a time.', 'start': 5852.996, 'duration': 5.922}, {'end': 5865.261, 'text': "It can open one locker and look inside, but it can't kind of take a step back, like we humans can, and look at all of the lockers,", 'start': 5858.978, 'duration': 6.283}], 'summary': 'Arrays are like lockers holding values, allowing a computer to process one at a time.', 'duration': 23.949, 'max_score': 5841.312, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I5841312.jpg'}, {'end': 6251.09, 'src': 'embed', 'start': 6222.561, 'weight': 0, 'content': [{'end': 6226.702, 'text': "Let's see if we can now reduce the process of sorting to something a little more algorithmic,", 'start': 6222.561, 'duration': 4.141}, {'end': 6231.664, 'text': "so that one we can be sure we're correct and not just kind of get lucky that everyone kind of figured it out and no one was left out.", 'start': 6226.702, 'duration': 4.962}, {'end': 6235.165, 'text': 'And two, then start to think about how efficient it is right?', 'start': 6231.944, 'duration': 3.221}, {'end': 6239.126, 'text': "Because if we've been gaining so much efficiency for the phone book, for our context,", 'start': 6235.205, 'duration': 3.921}, {'end': 6245.288, 'text': 'for Eric coming up Like we really should have been asking the whole time sure you save time with binary search and divide and conquer.', 'start': 6239.126, 'duration': 6.162}, {'end': 6251.09, 'text': 'But how much did it cost you to get to a point where you can use binary search and divide and conquer?', 'start': 6245.568, 'duration': 5.522}], 'summary': 'Discussing the need for an algorithmic sorting process and questioning its efficiency and cost.', 'duration': 28.529, 'max_score': 6222.561, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I6222561.jpg'}, {'end': 6654.673, 'src': 'embed', 'start': 6627.083, 'weight': 3, 'content': [{'end': 6629.843, 'text': 'And see how we actually got to that point.', 'start': 6627.083, 'duration': 2.76}, {'end': 6639.327, 'text': 'If I go ahead and pull up, not our lockers, but our answers here, let me propose that what we just did was essentially two algorithms.', 'start': 6629.883, 'duration': 9.444}, {'end': 6640.348, 'text': 'One has a name, bubble.', 'start': 6639.427, 'duration': 0.921}, {'end': 6642.669, 'text': 'And I was kind of deliberately kind of shoehorning the word in there.', 'start': 6640.388, 'duration': 2.281}, {'end': 6648.05, 'text': 'Bubble sort is just that comparative sort, pair by pair, fixing tiny little mistakes.', 'start': 6642.929, 'duration': 5.121}, {'end': 6650.831, 'text': 'But we needed to do it again and again and again.', 'start': 6648.29, 'duration': 2.541}, {'end': 6652.332, 'text': 'So those steps kind of add up.', 'start': 6651.151, 'duration': 1.181}, {'end': 6654.673, 'text': 'But we can express them as pseudocode.', 'start': 6652.352, 'duration': 2.321}], 'summary': 'The process involved two algorithms, including a bubble sort, and the steps can be expressed as pseudocode.', 'duration': 27.59, 'max_score': 6627.083, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I6627083.jpg'}, {'end': 6714.438, 'src': 'embed', 'start': 6685.45, 'weight': 4, 'content': [{'end': 6687.811, 'text': "and then just keep doing that until there's no one left to swap.", 'start': 6685.45, 'duration': 2.361}, {'end': 6689.991, 'text': 'And by definition, everyone is in order.', 'start': 6687.891, 'duration': 2.1}, {'end': 6693.612, 'text': 'Meanwhile, the second algorithm has a conventional name of selection sort.', 'start': 6690.311, 'duration': 3.301}, {'end': 6702.015, 'text': 'Selection sort is literally just that, where you actually select the smallest person or number of interest to you iteratively again and again.', 'start': 6693.692, 'duration': 8.323}, {'end': 6706.136, 'text': "And the number keeps getting bigger, but you start ignoring the people who you've already put into place.", 'start': 6702.035, 'duration': 4.101}, {'end': 6709.176, 'text': 'So the problem, similarly, is getting smaller and smaller.', 'start': 6706.456, 'duration': 2.72}, {'end': 6712.257, 'text': 'Just like in bubble sort, it was getting more and more sorted.', 'start': 6709.216, 'duration': 3.041}, {'end': 6714.438, 'text': 'The pseudocode for selection sort might look like this.', 'start': 6712.477, 'duration': 1.961}], 'summary': 'Selection sort iteratively selects smallest person/number, reducing problem size.', 'duration': 28.988, 'max_score': 6685.45, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I6685450.jpg'}], 'start': 5597.946, 'title': 'Sorting algorithms and efficiency', 'summary': 'Explores sorting algorithms, emphasizing on efficiency through examples, and discusses comparative sorting algorithms bubble sort and selection sort, highlighting their processes and reduction in comparisons and steps.', 'chapters': [{'end': 5930.003, 'start': 5597.946, 'title': 'Signaling errors and arrays', 'summary': "Explains how to signal errors using exit codes in the program, 'exit.c', and delves into the use of arrays as fundamental building blocks to solve problems algorithmically.", 'duration': 332.057, 'highlights': ["The program 'exit.c' implicitly wants the user to provide exactly two words at the prompt, signaling an error and returning 1 if this condition is not met. The program 'exit.c' expects two words at the prompt and signals an error by returning 1 if this condition is not met.", "The 'exit' command returns a value, which can be seen by typing 'echo $?' after running the program, allowing for the identification of the exit code (0 or 1) indicating program success or failure. The 'exit' command returns a value, which can be identified using 'echo $?' to determine the exit code (0 or 1) indicating program success or failure.", 'It is convention to exit from main by returning a non-zero value if anything goes wrong, where 0 indicates everything went well, which is useful for signaling errors in more complex programs. Exiting from main by returning a non-zero value is a convention for signaling errors in more complex programs, with 0 indicating successful execution.', "Arrays are described as fundamental building blocks to solve problems algorithmically, with the metaphor of a series of lockers containing values and the implication that a computer can only access one element at a time. Arrays are fundamental for solving problems algorithmically, likened to a series of lockers containing values, and highlighting the computer's limitation to access only one element at a time.", 'The efficiency of algorithms like searching in an ordered phone book is discussed, emphasizing the benefits of using arrays for storing and accessing data in sorted order. The efficiency of algorithms like searching in an ordered phone book is highlighted, underscoring the benefits of using arrays for storing and accessing data in sorted order.']}, {'end': 6255.671, 'start': 5930.684, 'title': 'Sorting algorithms and efficiency', 'summary': 'Discusses the concept of sorting algorithms, emphasizing on the efficiency gained by sorting information, demonstrated through examples of finding numbers behind doors and sorting humans in an array, highlighting the significance of efficient sorting algorithms for subsequent operations.', 'duration': 324.987, 'highlights': ['The significance of efficient sorting algorithms for subsequent operations, exemplified by finding numbers behind doors and sorting humans in an array. The chapter emphasizes the importance of efficient sorting algorithms by demonstrating the impact on subsequent operations, as shown through examples of finding numbers behind doors and sorting humans in an array.', 'Demonstration of efficient sorting algorithms through examples of finding numbers behind doors and sorting humans in an array. Efficient sorting algorithms are demonstrated through examples of finding numbers behind doors and sorting humans in an array, showcasing the practical application and significance of efficient sorting techniques.', 'Discussion on the efficiency gained by sorting information, emphasizing its impact on subsequent operations. The chapter discusses the efficiency gained by sorting information and emphasizes its impact on subsequent operations, highlighting the need for efficient sorting algorithms to optimize processes.']}, {'end': 6738.712, 'start': 6255.711, 'title': 'Comparative sorting algorithms', 'summary': 'Explores two comparative sorting algorithms, bubble sort and selection sort, using human volunteers to demonstrate the process, with bubble sort involving pair-wise comparisons and iterative swaps, and selection sort involving iterative selection of the smallest element and macroscopic swaps, ultimately reducing the number of comparisons and steps with each iteration.', 'duration': 483.001, 'highlights': ['The chapter demonstrates the Bubble Sort algorithm, which involves pair-wise comparisons of humans and iterative swaps, resulting in a decreasing number of comparisons and steps with each iteration.', 'It also showcases the Selection Sort algorithm, where the smallest element is selected iteratively, leading to a reduction in the number of comparisons and steps as elements are put into place.', 'The pseudocode for Bubble Sort involves iterating through the list and swapping adjacent elements if they are out of order, leading to an eventual sorted list with no remaining swaps.', 'On the other hand, the pseudocode for Selection Sort entails repeatedly selecting the smallest element and swapping it with the current position, eventually resulting in a sorted list with elements in their correct places.']}], 'duration': 1140.766, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I5597946.jpg', 'highlights': ['Efficient sorting algorithms are crucial for subsequent operations, demonstrated through practical examples.', "Arrays are fundamental for solving problems algorithmically, with the computer's limitation to access only one element at a time.", 'The efficiency gained by sorting information has a significant impact on subsequent operations, emphasizing the need for efficient sorting algorithms.', 'Demonstration of Bubble Sort algorithm involves pair-wise comparisons and iterative swaps, resulting in a decreasing number of comparisons and steps with each iteration.', 'Showcasing the Selection Sort algorithm, where the smallest element is selected iteratively, leading to a reduction in the number of comparisons and steps as elements are put into place.']}, {'end': 7649.39, 'segs': [{'end': 7012.552, 'src': 'embed', 'start': 6984.799, 'weight': 3, 'content': [{'end': 6990.106, 'text': 'Only the third algorithm, the divide and conquer, splitting the phone book was a fundamentally different shape.', 'start': 6984.799, 'duration': 5.307}, {'end': 6997.295, 'text': "And so, even though we didn't use this fancy phrasing a couple of weeks ago, these first two algorithms, one page at a time, two pages at a time.", 'start': 6990.406, 'duration': 6.889}, {'end': 7000.199, 'text': "Eh, they're on the order of n.", 'start': 6997.896, 'duration': 2.303}, {'end': 7003.022, 'text': 'Technically, yes, n versus n divided by 2.', 'start': 7000.199, 'duration': 2.823}, {'end': 7006.706, 'text': 'But we only care about the dominating factor, the variable n.', 'start': 7003.022, 'duration': 3.684}, {'end': 7012.552, 'text': "We can throw away everything in the denominator, and we can throw away everything that's smaller than the biggest term, which in this case is just n.", 'start': 7006.706, 'duration': 5.846}], 'summary': 'The divide and conquer algorithm demonstrated a fundamentally different shape, with the first two algorithms being on the order of n, with the dominating factor being variable n.', 'duration': 27.753, 'max_score': 6984.799, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I6984799.jpg'}, {'end': 7078.298, 'src': 'embed', 'start': 7048.128, 'weight': 1, 'content': [{'end': 7050.528, 'text': 'That might be a constant time algorithm, for instance.', 'start': 7048.128, 'duration': 2.4}, {'end': 7052.489, 'text': 'So those are the lowest you can go.', 'start': 7050.568, 'duration': 1.921}, {'end': 7058.071, 'text': "And then there's somewhere even in between here that we might aspire to with certain other algorithms.", 'start': 7052.529, 'duration': 5.542}, {'end': 7065.155, 'text': "So in fact, let's just see if just a moment, let's just see if we can do this a little more succinctly.", 'start': 7058.291, 'duration': 6.864}, {'end': 7070.816, 'text': "Let's go ahead and use arrays in just one final way using merge sort.", 'start': 7065.535, 'duration': 5.281}, {'end': 7078.298, 'text': 'So it turns out, using an array, we can actually do something pretty powerfully so long as we allow ourselves a couple of arrays.', 'start': 7071.216, 'duration': 7.082}], 'summary': 'Discussion on constant time algorithm and merge sort using arrays.', 'duration': 30.17, 'max_score': 7048.128, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I7048128.jpg'}, {'end': 7316.84, 'src': 'embed', 'start': 7286.635, 'weight': 2, 'content': [{'end': 7287.856, 'text': 'What comes next? Right half.', 'start': 7286.635, 'duration': 1.221}, {'end': 7294.439, 'text': '3 and 1, well, left half is sorted, right half is sorted, 1 and 3.', 'start': 7288.816, 'duration': 5.623}, {'end': 7303.343, 'text': 'All right, now how do I merge these? 6, 8, 1, 3, which element should obviously come first? 1, then 3, then 6, then 8.', 'start': 7294.439, 'duration': 8.904}, {'end': 7306.044, 'text': 'And then lastly, I have two lists of size 4.', 'start': 7303.343, 'duration': 2.701}, {'end': 7308.125, 'text': 'Let me give myself a little more space, one more array.', 'start': 7306.044, 'duration': 2.081}, {'end': 7316.84, 'text': 'Now let me go ahead and put 1 and 2 and 3 and 4 and 5 and 6 and 7 and 8.', 'start': 7308.686, 'duration': 8.154}], 'summary': 'Sorting and merging numbers in two halves, then into a larger array.', 'duration': 30.205, 'max_score': 7286.635, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I7286635.jpg'}, {'end': 7595.317, 'src': 'heatmap', 'start': 7418.809, 'weight': 0.725, 'content': [{'end': 7426.014, 'text': 'The total arithmetic here in question is one of those other values on our little cheat sheet, which looked like this.', 'start': 7418.809, 'duration': 7.205}, {'end': 7434.7, 'text': 'In our other cheat sheet, recall that we had formulas that looked like this, not just n squared and n and log n and 1.', 'start': 7426.614, 'duration': 8.086}, {'end': 7437.782, 'text': 'We had this one in the middle, n times log n.', 'start': 7434.7, 'duration': 3.082}, {'end': 7440.123, 'text': "So again, we're kind of jumping around here.", 'start': 7438.542, 'duration': 1.581}, {'end': 7442.664, 'text': 'But again, each number moves log n places.', 'start': 7440.163, 'duration': 2.501}, {'end': 7444.084, 'text': "There's n total numbers.", 'start': 7442.924, 'duration': 1.16}, {'end': 7448.326, 'text': 'So n times log n is just, by definition, n log n.', 'start': 7444.424, 'duration': 3.902}, {'end': 7455.628, 'text': 'But why is this sorted this way? Well, log n, recall from week 0 with the phone book example, the green curve is definitely smaller than n.', 'start': 7448.326, 'duration': 7.302}, {'end': 7456.749, 'text': 'n was the straight lines.', 'start': 7455.628, 'duration': 1.121}, {'end': 7458.569, 'text': 'Log n was the green curved one.', 'start': 7457.029, 'duration': 1.54}, {'end': 7461.811, 'text': 'So this indeed belongs in between, because this is n times n.', 'start': 7458.83, 'duration': 2.981}, {'end': 7462.671, 'text': 'This is n.', 'start': 7461.811, 'duration': 0.86}, {'end': 7464.852, 'text': 'This is n times something smaller than n.', 'start': 7462.671, 'duration': 2.181}, {'end': 7467.273, 'text': "So what's the actual implication??", 'start': 7465.672, 'duration': 1.601}, {'end': 7474.78, 'text': 'Well, if we were to run these algorithms side by side and actually compare them with something like this,', 'start': 7467.314, 'duration': 7.466}, {'end': 7481.543, 'text': 'let me go ahead and compare These algorithms using this demo here.', 'start': 7474.78, 'duration': 6.763}, {'end': 7485.645, 'text': "if I go ahead and hit Play, we'll see that the bars in this chart are actually horizontal.", 'start': 7481.543, 'duration': 4.102}, {'end': 7487.926, 'text': 'And the small bars represent small numbers.', 'start': 7486.025, 'duration': 1.901}, {'end': 7489.726, 'text': 'Large bars represent long numbers.', 'start': 7488.146, 'duration': 1.58}, {'end': 7492.167, 'text': 'And then each of these is going to run a different algorithm.', 'start': 7490.047, 'duration': 2.12}, {'end': 7496.989, 'text': "Selection sort on the left, bubble sort in the middle, merge sort, as we'll now call it, on the right.", 'start': 7492.247, 'duration': 4.742}, {'end': 7500.891, 'text': "And here's how long each of them take to sort those values.", 'start': 7497.95, 'duration': 2.941}, {'end': 7506.255, 'text': "Done Bubble's still going.", 'start': 7503.212, 'duration': 3.043}, {'end': 7507.695, 'text': "Selection's still going.", 'start': 7506.535, 'duration': 1.16}, {'end': 7513.078, 'text': "And so that's the appreciable difference, albeit with a small demo, between n squared and something like log n.", 'start': 7507.755, 'duration': 5.323}, {'end': 7514.178, 'text': 'And so what have we done here?', 'start': 7513.078, 'duration': 1.1}, {'end': 7519.961, 'text': 'We really really really got into the weeds of what arrays can actually do for us and what the relationships are with strings,', 'start': 7514.238, 'duration': 5.723}, {'end': 7522.842, 'text': 'because all of it kind of reduces to just things being back to back, to back to back.', 'start': 7519.961, 'duration': 2.881}, {'end': 7529.985, 'text': "But now that we kind of come back and we'll continue along this trajectory next time we'll be able to talk at a much higher level about what's actually going on.", 'start': 7523.062, 'duration': 6.923}, {'end': 7532.066, 'text': 'And we can now take this even further.', 'start': 7530.285, 'duration': 1.781}, {'end': 7535.869, 'text': 'by applying other sort of forms of media to these same kinds of questions.', 'start': 7532.526, 'duration': 3.343}, {'end': 7537.63, 'text': "And we'll conclude it's about 60 seconds long.", 'start': 7535.889, 'duration': 1.741}, {'end': 7539.612, 'text': 'These bars are vertical instead of horizontal.', 'start': 7537.831, 'duration': 1.781}, {'end': 7545.137, 'text': "And what you'll see here is a visualization of various sorting algorithms, among them selection, sort, bubble sort and merge sort,", 'start': 7539.632, 'duration': 5.505}, {'end': 7554.064, 'text': 'and a whole assortment of others, each of which has even a different sound to it because of the speed and the pattern by which it actually operates.', 'start': 7545.137, 'duration': 8.927}, {'end': 7555.005, 'text': "So let's take a quick look.", 'start': 7554.104, 'duration': 0.901}, {'end': 7571.034, 'text': 'You can see how the larger elements are indeed bubbling up to the top.', 'start': 7567.532, 'duration': 3.502}, {'end': 7573.736, 'text': "Periodicity or the cycle that it's going in.", 'start': 7571.795, 'duration': 1.941}, {'end': 7576.677, 'text': "And there's less and less and less and less work to do until almost.", 'start': 7573.836, 'duration': 2.841}, {'end': 7595.317, 'text': 'This is selection sort now.', 'start': 7593.936, 'duration': 1.381}], 'summary': 'N log n is a key value in sorting algorithms, with visual demos showing its efficiency compared to n squared.', 'duration': 176.508, 'max_score': 7418.809, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I7418809.jpg'}, {'end': 7519.961, 'src': 'embed', 'start': 7490.047, 'weight': 0, 'content': [{'end': 7492.167, 'text': 'And then each of these is going to run a different algorithm.', 'start': 7490.047, 'duration': 2.12}, {'end': 7496.989, 'text': "Selection sort on the left, bubble sort in the middle, merge sort, as we'll now call it, on the right.", 'start': 7492.247, 'duration': 4.742}, {'end': 7500.891, 'text': "And here's how long each of them take to sort those values.", 'start': 7497.95, 'duration': 2.941}, {'end': 7506.255, 'text': "Done Bubble's still going.", 'start': 7503.212, 'duration': 3.043}, {'end': 7507.695, 'text': "Selection's still going.", 'start': 7506.535, 'duration': 1.16}, {'end': 7513.078, 'text': "And so that's the appreciable difference, albeit with a small demo, between n squared and something like log n.", 'start': 7507.755, 'duration': 5.323}, {'end': 7514.178, 'text': 'And so what have we done here?', 'start': 7513.078, 'duration': 1.1}, {'end': 7519.961, 'text': 'We really really really got into the weeds of what arrays can actually do for us and what the relationships are with strings,', 'start': 7514.238, 'duration': 5.723}], 'summary': 'Comparison of sorting algorithms: selection sort, bubble sort, and merge sort, demonstrating time differences between n squared and log n.', 'duration': 29.914, 'max_score': 7490.047, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I7490047.jpg'}, {'end': 7571.034, 'src': 'embed', 'start': 7539.632, 'weight': 4, 'content': [{'end': 7545.137, 'text': "And what you'll see here is a visualization of various sorting algorithms, among them selection, sort, bubble sort and merge sort,", 'start': 7539.632, 'duration': 5.505}, {'end': 7554.064, 'text': 'and a whole assortment of others, each of which has even a different sound to it because of the speed and the pattern by which it actually operates.', 'start': 7545.137, 'duration': 8.927}, {'end': 7555.005, 'text': "So let's take a quick look.", 'start': 7554.104, 'duration': 0.901}, {'end': 7571.034, 'text': 'You can see how the larger elements are indeed bubbling up to the top.', 'start': 7567.532, 'duration': 3.502}], 'summary': 'Visualization of sorting algorithms including selection, bubble, and merge sort, showing larger elements bubbling up.', 'duration': 31.402, 'max_score': 7539.632, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I7539632.jpg'}], 'start': 6739.412, 'title': 'Sorting algorithms and efficiency', 'summary': "Delves into the comparison of bubble sort and selection sort, emphasizing their o(n^2) time complexity, and discusses various algorithms and techniques for improved efficiency, including merge sort's step-by-step explanation and visualizations of logarithmic sorting algorithms.", 'chapters': [{'end': 6946.488, 'start': 6739.412, 'title': 'Comparison of sorting algorithms', 'summary': 'Discusses the comparison of bubble sort and selection sort, concluding that both algorithms have a time complexity of approximately o(n^2) and emphasizes the significance of big o notation in evaluating algorithm efficiency.', 'duration': 207.076, 'highlights': ['Both bubble sort and selection sort have a time complexity of approximately O(n^2), with the biggest term dominating the other terms as the input size increases.', 'The total number of steps for selection sort can be expressed as n squared divided by 2 minus n over 2, which simplifies to roughly O(n^2) as n increases, demonstrating the significance of big O notation in algorithm evaluation.', 'The example with a million people on stage illustrates that the time complexity of selection sort is on the order of n squared, emphasizing the practical significance of big O notation in assessing algorithm efficiency.', "The significance of big O notation lies in describing, with a wave of the hand but some good intuition, how fast or slow an algorithm is, providing a useful tool for evaluating and comparing different algorithms' efficiencies."]}, {'end': 7103.844, 'start': 6947.108, 'title': 'Algorithmic efficiency and complexity', 'summary': 'Discusses different algorithms, including linear, logarithmic, and constant time, emphasizing the efficiencies achieved through techniques like divide and conquer and leveraging arrays for improved performance.', 'duration': 156.736, 'highlights': ['The divide and conquer algorithm is fundamentally different and demonstrates a logarithmic type function, offering improved efficiency compared to linear algorithms. The divide and conquer algorithm, with its fundamentally different shape, demonstrates a logarithmic type function, offering improved efficiency compared to linear algorithms.', 'Constant time algorithms, such as opening a phone book, demonstrate the lowest complexity and are independent of the number of elements, providing the most efficient performance. Constant time algorithms, such as opening a phone book, demonstrate the lowest complexity and are independent of the number of elements, providing the most efficient performance.', 'Utilizing arrays, particularly with techniques like merge sort, can significantly improve algorithmic efficiency by leveraging additional arrays for shuffling and comparison, surpassing the performance of single-array methods like bubble sort and selection sort. Utilizing arrays, particularly with techniques like merge sort, can significantly improve algorithmic efficiency by leveraging additional arrays for shuffling and comparison, surpassing the performance of single-array methods like bubble sort and selection sort.']}, {'end': 7359.897, 'start': 7103.844, 'title': 'Merge sort algorithm explanation', 'summary': 'Explains the merge sort algorithm through a step-by-step verbal walkthrough, illustrating the process of sorting a randomly sorted array of 8 elements, emphasizing the concept of merging sorted halves and analyzing the number of times each element changes locations.', 'duration': 256.053, 'highlights': ['The chapter illustrates the process of sorting a randomly sorted array of 8 elements using the merge sort algorithm, emphasizing the concept of merging sorted halves. Illustrates the merge sort algorithm; Emphasizes the concept of merging sorted halves; Involves sorting a randomly sorted array of 8 elements.', 'The speaker verbally walks through the step-by-step process of dividing the array, sorting individual halves, and merging them, providing a clear explanation of the merge sort algorithm. Verbally walks through the step-by-step process; Provides a clear explanation of the merge sort algorithm; Involves dividing the array, sorting individual halves, and merging them.', 'The chapter analyzes the number of times each element changes locations during the sorting process, highlighting the concept of elements moving 1, 2, or 3 spots in different arrays. Analyzes the number of times each element changes locations; Highlights the concept of elements moving 1, 2, or 3 spots in different arrays; Emphasizes the analysis of the movement of elements during sorting.']}, {'end': 7649.39, 'start': 7359.958, 'title': 'Logarithmic sorting algorithms', 'summary': 'Discusses the concept of logarithmic sorting algorithms, emphasizing the relationship between the number of elements and the number of operations, as well as demonstrating the efficiency of different sorting algorithms through visualizations.', 'duration': 289.432, 'highlights': ['The relationship between the number of elements and the number of operations in sorting algorithms is described using the concept of logarithm, where dividing the elements by the same proportional amount results in a logarithmic function, denoted as log n. The concept of logarithmic sorting algorithms is introduced, highlighting the relationship between the number of elements and the number of operations, represented by the logarithm function log n.', 'The time complexity of sorting algorithms, particularly the n log n complexity, is explained in comparison to other common complexities such as n squared, and the efficiency is visually demonstrated through a comparison of sorting algorithms using a demo. The time complexity of sorting algorithms, specifically the n log n complexity, is compared to other common complexities like n squared, and the efficiency is visually demonstrated through a comparison of sorting algorithms using a demo.', 'Visualizations of sorting algorithms, including selection sort, bubble sort, and merge sort, are presented, showcasing the distinct patterns and speeds of operation, providing a practical understanding of algorithmic efficiency. Visualizations of sorting algorithms, such as selection sort, bubble sort, and merge sort, are showcased, offering insights into their distinct patterns and speeds of operation for a practical understanding of algorithmic efficiency.']}], 'duration': 909.978, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/ba7e4mksR5I/pics/ba7e4mksR5I6739412.jpg', 'highlights': ['The time complexity of sorting algorithms, particularly the n log n complexity, is explained in comparison to other common complexities such as n squared, and the efficiency is visually demonstrated through a comparison of sorting algorithms using a demo.', 'Utilizing arrays, particularly with techniques like merge sort, can significantly improve algorithmic efficiency by leveraging additional arrays for shuffling and comparison, surpassing the performance of single-array methods like bubble sort and selection sort.', 'The chapter illustrates the process of sorting a randomly sorted array of 8 elements using the merge sort algorithm, emphasizing the concept of merging sorted halves.', 'The divide and conquer algorithm is fundamentally different and demonstrates a logarithmic type function, offering improved efficiency compared to linear algorithms.', 'Visualizations of sorting algorithms, including selection sort, bubble sort, and merge sort, are presented, showcasing the distinct patterns and speeds of operation, providing a practical understanding of algorithmic efficiency.']}], 'highlights': ["The make command automates the process of linking CS50's library with the program, making the compilation process more efficient and less tedious.", 'The preprocessing step in the compilation process involves handling preprocessor directives demarcated by a hash, which are processed before everything else.', 'RAM vs. hard drives: RAM is ephemeral and faster, used when the power is on or the battery is charged, while hard drives store files permanently.', 'The benefits of using arrays for efficiently storing multiple values are explained, emphasizing the improved memory management and scalability they offer compared to using individual variables.', 'Explaining the benefits of caching the answer of a function call by using a variable instead of repeatedly calling the function. By caching the length of the string in a variable, it reduces the need to repeatedly call the strlen function, improving performance and efficiency.', 'The process of automatic capitalization in text editors is based on leveraging the patterns of character numbers, where capital A is 65 and lowercase a is 97, among others.', 'The importance of secure communication through cryptography is demonstrated by the inadequacy of simple encoding methods like ASCII, which can be easily decoded by anyone familiar with the system.', 'Efficient sorting algorithms are crucial for subsequent operations, demonstrated through practical examples.', 'The time complexity of sorting algorithms, particularly the n log n complexity, is explained in comparison to other common complexities such as n squared, and the efficiency is visually demonstrated through a comparison of sorting algorithms using a demo.']}