title
CS50 2021 in HDR - Lecture 2 - Arrays

description
This is CS50, Harvard University's Introduction to the intellectual enterprises of computer science and the art of programming. Enroll for free at https://cs50.edx.org/. Slides, source code, and more at https://cs50.harvard.edu/x. Playlist at https://www.youtube.com/playlist?list=PLhQjrBD2T383f9scHRNYJkior2VvYjpSL. TABLE OF CONTENTS 00:00:00 - Introduction 00:01:17 - Make 00:02:56 - Clang 00:10:44 - Compiling 00:22:40 - Debugging 00:24:34 - buggy.c 00:26:08 - printf 00:28:08 - debug50 00:33:32 - Rubber Duck Debugging 00:36:00 - get_negative_int 00:39:31 - Step Into 00:40:33 - Types 00:43:17 - Memory 00:45:22 - scores.c 00:50:50 - Arrays 01:01:13 - Array of Characters 01:08:23 - NUL Character 01:18:22 - length.c 01:23:35 - strlen 01:24:14 - Manual Pages 01:27:48 - ASCII 01:29:24 - string.c 01:35:37 - uppercase.c 01:40:33 - islower 01:43:35 - toupper 01:46:42 - Command-line Arguments 01:47:39 - argc and argv 01:56:13 - Exit Status 02:01:24 - Readability 02:04:12 - Cryptography *** This is CS50, Harvard University's introduction to the intellectual enterprises of computer science and the art of programming. *** HOW TO SUBSCRIBE http://www.youtube.com/subscription_center?add_user=cs50tv HOW TO TAKE CS50 edX: https://cs50.edx.org/ Harvard Extension School: https://cs50.harvard.edu/extension Harvard Summer School: https://cs50.harvard.edu/summer OpenCourseWare: https://cs50.harvard.edu/x HOW TO JOIN CS50 COMMUNITIES Discord: https://discord.gg/cs50 Ed: https://cs50.harvard.edu/x/ed Facebook Group: https://www.facebook.com/groups/cs50/ Faceboook Page: https://www.facebook.com/cs50/ GitHub: https://github.com/cs50 Gitter: https://gitter.im/cs50/x Instagram: https://instagram.com/cs50 LinkedIn Group: https://www.linkedin.com/groups/7437240/ LinkedIn Page: https://www.linkedin.com/school/cs50/ Medium: https://cs50.medium.com/ Quora: https://www.quora.com/topic/CS50 Reddit: https://www.reddit.com/r/cs50/ Slack: https://cs50.edx.org/slack Snapchat: https://www.snapchat.com/add/cs50 SoundCloud: https://soundcloud.com/cs50 Stack Exchange: https://cs50.stackexchange.com/ TikTok: https://www.tiktok.com/@cs50 Twitter: https://twitter.com/cs50 YouTube: http://www.youtube.com/cs50 HOW TO FOLLOW DAVID J. MALAN Facebook: https://www.facebook.com/dmalan GitHub: https://github.com/dmalan Instagram: https://www.instagram.com/davidjmalan/ LinkedIn: https://www.linkedin.com/in/malan/ Quora: https://www.quora.com/profile/David-J-Malan TikTok: https://www.tiktok.com/@davidjmalan Twitter: https://twitter.com/davidjmalan *** CS50 SHOP https://cs50.harvardshop.com/ *** LICENSE CC BY-NC-SA 4.0 Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Public License https://creativecommons.org/licenses/by-nc-sa/4.0/ David J. Malan https://cs.harvard.edu/malan malan@harvard.edu

detail
{'title': 'CS50 2021 in HDR - Lecture 2 - Arrays', 'heatmap': [{'end': 2844.241, 'start': 2755.867, 'weight': 0.74}, {'end': 5069.795, 'start': 4907.176, 'weight': 0.737}, {'end': 6605.796, 'start': 6444.81, 'weight': 1}, {'end': 6757.09, 'start': 6677.838, 'weight': 0.864}], 'summary': 'The 2021 cs50 lecture on arrays covers c language basics, code compilation, debugging techniques, data types, program design, memory representation, strings manipulation, efficient variable declaration, and c programming topics, addressing various concepts and techniques in programming.', 'chapters': [{'end': 638.235, 'segs': [{'end': 320.883, 'src': 'embed', 'start': 286.009, 'weight': 6, 'content': [{'end': 290.874, 'text': 'And I do have hello now, so dot slash hello, voila, runs hello world again.', 'start': 286.009, 'duration': 4.865}, {'end': 293.035, 'text': 'And let me go ahead and remove this file.', 'start': 291.494, 'duration': 1.541}, {'end': 300.239, 'text': 'I could, of course, resort to using the Explorer on the left-hand side, which I am in the habit of closing just to give us more room to see.', 'start': 293.135, 'duration': 7.104}, {'end': 304.121, 'text': 'But I could go ahead and right-click or Control-click on a.out if I want to get rid of it.', 'start': 300.519, 'duration': 3.602}, {'end': 307.063, 'text': 'Or again, let me focus on the command line interface.', 'start': 304.241, 'duration': 2.822}, {'end': 309.965, 'text': "And I can use, anyone recall? We didn't really use it much.", 'start': 307.163, 'duration': 2.802}, {'end': 320.883, 'text': 'But what command removes a file? So rm for remove, rm, a.out, Enter, remove regular file, a.out, y for yes, Enter.', 'start': 310.045, 'duration': 10.838}], 'summary': "Using command line interface to remove file a.out using 'rm' command.", 'duration': 34.874, 'max_score': 286.009, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE286009.jpg'}, {'end': 383.846, 'src': 'embed', 'start': 354.233, 'weight': 2, 'content': [{'end': 359.174, 'text': "If I want to compile this thing myself with Clang using that same lesson learned, all right, let's do it.", 'start': 354.233, 'duration': 4.941}, {'end': 365.017, 'text': 'clang-o hello, just so I get a better name for the program, hello.c.', 'start': 359.574, 'duration': 5.443}, {'end': 370.34, 'text': 'Enter And a new error pops up that some of you might have encountered on your own.', 'start': 365.677, 'duration': 4.663}, {'end': 372.14, 'text': "So it's a bit arcane here.", 'start': 370.76, 'duration': 1.38}, {'end': 375.942, 'text': "And there's this mention of a cryptic looking path with temp for temporary there.", 'start': 372.221, 'duration': 3.721}, {'end': 377.803, 'text': 'But somehow my issues in main.', 'start': 376.263, 'duration': 1.54}, {'end': 383.846, 'text': 'as we can see here, it somehow relates to hello.c, even though we might not have seen this language last time in class.', 'start': 377.803, 'duration': 6.043}], 'summary': 'Compiling with clang using the lesson learned, encountered new error related to hello.c', 'duration': 29.613, 'max_score': 354.233, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE354233.jpg'}, {'end': 608.888, 'src': 'embed', 'start': 582.853, 'weight': 0, 'content': [{'end': 587.055, 'text': 'Oh, what does the dash o mean? So dash o is shorthand for the English word output.', 'start': 582.853, 'duration': 4.202}, {'end': 592.297, 'text': 'And so dash o is telling Clang to please output a file called hello,', 'start': 587.135, 'duration': 5.162}, {'end': 600.181, 'text': 'because the next thing I wrote after the command line recall was Clang dash o hello, then the name of the file, then dash lcs50..', 'start': 592.297, 'duration': 7.884}, {'end': 604.684, 'text': 'This is where these commands do get and stay fairly arcane.', 'start': 601.101, 'duration': 3.583}, {'end': 607.207, 'text': "It's just through muscle, memory and practice that you'll start to remember.", 'start': 604.724, 'duration': 2.483}, {'end': 608.888, 'text': 'oh, what are the other commands that you?', 'start': 607.207, 'duration': 1.681}], 'summary': 'Dash o is shorthand for output, used with clang to create file hello.', 'duration': 26.035, 'max_score': 582.853, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE582853.jpg'}], 'start': 78.086, 'title': 'C language basics and compiling with clang', 'summary': 'Covers c language basics, including compiling c code with clang and linking libraries, such as cs50, and addressing challenges in linking standard i.o. it also discusses automating the process using make.', 'chapters': [{'end': 331.288, 'start': 78.086, 'title': 'Understanding c language basics', 'summary': 'Covers the basics of programming in c, explaining the process of compiling c code into machine code using the make command and the clang compiler, as well as customizing program names and using command line arguments to modify program behavior.', 'duration': 253.202, 'highlights': ['The process of compiling C code into machine code using the make command and the Clang compiler is explained. ', "The customization of program names using command line arguments and using the Clang compiler to specify the outputted program's name is demonstrated. ", "The removal of a file using the command line interface is illustrated with the 'rm' command. "]}, {'end': 638.235, 'start': 331.288, 'title': 'Compiling with clang and linking libraries', 'summary': 'Discusses the process of compiling a program with clang, including linking in external libraries like cs50 and the challenges related to linking standard i.o., highlighting the need for additional commands to link libraries and the automation of this process using make.', 'duration': 306.947, 'highlights': ['The process of compiling a program with Clang and linking in external libraries like CS50 is discussed, emphasizing the need for additional commands to link libraries and the automation of this process using make.', 'The challenges related to linking standard I.O. are highlighted, explaining that standard I.O. is built in and works for free, unlike CS50, which needs to be specifically linked.', 'The need for additional commands to link libraries, such as using -lcs50 to link in the zeros and ones that collectively implement functions like getString and printf, is explained.', 'The automation of the process of linking libraries using make is mentioned, emphasizing its role in automating the compilation process and handling increasingly complex programs.']}], 'duration': 560.149, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE78086.jpg', 'highlights': ['The automation of the process of linking libraries using make is mentioned, emphasizing its role in automating the compilation process and handling increasingly complex programs.', 'The process of compiling a program with Clang and linking in external libraries like CS50 is discussed, emphasizing the need for additional commands to link libraries and the automation of this process using make.', 'The process of compiling C code into machine code using the make command and the Clang compiler is explained.', "The customization of program names using command line arguments and using the Clang compiler to specify the outputted program's name is demonstrated.", 'The need for additional commands to link libraries, such as using -lcs50 to link in the zeros and ones that collectively implement functions like getString and printf, is explained.', 'The challenges related to linking standard I.O. are highlighted, explaining that standard I.O. is built in and works for free, unlike CS50, which needs to be specifically linked.', "The removal of a file using the command line interface is illustrated with the 'rm' command."]}, {'end': 1352.064, 'segs': [{'end': 703.05, 'src': 'embed', 'start': 675.748, 'weight': 1, 'content': [{'end': 678.53, 'text': "You actually do have this bottom-up understanding of what's going on.", 'start': 675.748, 'duration': 2.782}, {'end': 684.455, 'text': "So when we say you've been compiling your code with make, That's a bit of an oversimplification.", 'start': 678.931, 'duration': 5.524}, {'end': 690.46, 'text': "Technically, every time you compile your code, you're having the computer actually do four distinct things for you.", 'start': 684.556, 'duration': 5.904}, {'end': 695.844, 'text': "And this is not four distinct things that you need to sort of memorize and remember every time you run your program what's happening.", 'start': 690.48, 'duration': 5.364}, {'end': 703.05, 'text': "But it helps to sort of break it down into building blocks as to how we're getting from source code, like C, into zeros and ones.", 'start': 696.304, 'duration': 6.746}], 'summary': 'Compiling code involves four distinct processes, aiding in understanding source code transformation into zeros and ones.', 'duration': 27.302, 'max_score': 675.748, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE675748.jpg'}, {'end': 769.938, 'src': 'embed', 'start': 741.476, 'weight': 3, 'content': [{'end': 745.879, 'text': "It's a fancy way of saying they're handled special versus the rest of your code.", 'start': 741.476, 'duration': 4.403}, {'end': 756.127, 'text': "In fact, if we focus on CS50.h, recall from last week that I provided a hint as to what's actually in CS50.h, among other things.", 'start': 746.219, 'duration': 9.908}, {'end': 764.433, 'text': 'Like what was the one salient thing that I said was in CS50.h and therefore why we were including it in the first place?', 'start': 756.647, 'duration': 7.786}, {'end': 769.938, 'text': 'So get string, specifically the prototype for get string.', 'start': 765.856, 'duration': 4.082}], 'summary': 'Cs50.h handles get string prototype for special code.', 'duration': 28.462, 'max_score': 741.476, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE741476.jpg'}, {'end': 857.303, 'src': 'embed', 'start': 827.197, 'weight': 4, 'content': [{'end': 831.72, 'text': 'getString, not surprisingly, has a return value, and it returns a string.', 'start': 827.197, 'duration': 4.523}, {'end': 835.462, 'text': 'So literally, that line and a bunch of others are in CS50.h.', 'start': 832.22, 'duration': 3.242}, {'end': 841.847, 'text': 'And so rather than you all having to copy paste the prototype, you can just trust that CS50 figured out what it is.', 'start': 835.603, 'duration': 6.244}, {'end': 844.77, 'text': 'You can include CS50.h and the compiler.', 'start': 842.188, 'duration': 2.582}, {'end': 847.993, 'text': 'is going to go find that prototype for you.', 'start': 845.47, 'duration': 2.523}, {'end': 849.475, 'text': 'Same thing in standard I-O.', 'start': 848.393, 'duration': 1.082}, {'end': 857.303, 'text': 'Someone else, what must clearly be in standard I-O dot H, among other stuff, that motivates our including standard I-O dot H2? Yeah.', 'start': 849.495, 'duration': 7.808}], 'summary': 'Cs50.h and standard i-o.h provide return values and prototypes for string functions.', 'duration': 30.106, 'max_score': 827.197, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE827197.jpg'}, {'end': 936.665, 'src': 'embed', 'start': 910.456, 'weight': 0, 'content': [{'end': 915.081, 'text': 'thereby teaching the compiler that getString and printf will eventually exist somewhere.', 'start': 910.456, 'duration': 4.625}, {'end': 922.729, 'text': "So that's the preprocessing step whereby, again, it's just doing a find and replace of anything that starts with hash include.", 'start': 915.762, 'duration': 6.967}, {'end': 927.555, 'text': "It's plugging in the files there so that you essentially get all the prototypes you need automatically.", 'start': 923.21, 'duration': 4.345}, {'end': 936.665, 'text': "OK, what does it mean then to compile the results? Because at this point in the story, your code now looks like this in the computer's memory.", 'start': 929.238, 'duration': 7.427}], 'summary': 'Preprocessing step adds prototypes to code for efficient compilation.', 'duration': 26.209, 'max_score': 910.456, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE910456.jpg'}], 'start': 638.755, 'title': 'C code compilation', 'summary': 'Discusses the four automatic processes involved in compiling c code, the relationship between source code and assembly language, the basic computer instructions understood by cpus, with an emphasis on preprocessing and compiling steps. it also explains the process of compiling and linking code, highlighting differences between windows and mac programs, the steps of assembling code, and the role of different files in the compilation process.', 'chapters': [{'end': 1077.685, 'start': 638.755, 'title': 'Understanding c code compilation', 'summary': 'Discusses the four automatic processes involved in compiling c code, the relationship between source code and assembly language, and the basic computer instructions understood by cpus, with an emphasis on the preprocessing and compiling steps.', 'duration': 438.93, 'highlights': ['The chapter discusses the four automatic processes involved in compiling C code, which include preprocessing, compiling, assembling, and linking, with an emphasis on the preprocessing and compiling steps.', 'It explains the relationship between the C source code and the assembly language output, highlighting that the assembly language output still contains references to the main function, get string, and printf.', 'The transcript emphasizes the basic computer instructions understood by CPUs, which include addition, subtraction, division, multiplication, moving into memory, loading from memory, and printing to the screen.']}, {'end': 1352.064, 'start': 1077.685, 'title': 'Compiling and linking process', 'summary': 'Explains the process of compiling and linking code, highlighting the differences between windows and mac programs, the steps of assembling code, and the role of different files in the compilation process.', 'duration': 274.379, 'highlights': ['The commands and instructions for Windows and Mac programs are different, necessitating distinct steps in compiling and linking code. The reason why a program sold for a Windows computer cannot run on a Mac, or vice versa, is because the commands and instructions understood by those two products are actually different.', 'The process of assembling code involves converting assembly language into machine code, which is represented as zeros and ones. To assemble code, the assembly language generated from the source code is turned into zeros and ones, representing the final step in the process.', "The compilation process involves combining the zeros and ones from different files and linking them together into one single file. The linking step combines the zeros and ones from different programmers' code into one single file, such as 'hello' or 'a.out', through a linking command."]}], 'duration': 713.309, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE638755.jpg', 'highlights': ['The chapter discusses the four automatic processes involved in compiling C code: preprocessing, compiling, assembling, and linking.', 'The relationship between the C source code and the assembly language output is explained, highlighting references to main function, get string, and printf.', 'Basic computer instructions understood by CPUs include addition, subtraction, division, multiplication, moving into memory, loading from memory, and printing to the screen.', 'Commands and instructions for Windows and Mac programs differ, requiring distinct steps in compiling and linking code.', 'Assembling code involves converting assembly language into machine code represented as zeros and ones.', 'The compilation process combines zeros and ones from different files and links them together into one single file.']}, {'end': 2416.915, 'segs': [{'end': 1397.525, 'src': 'embed', 'start': 1370.962, 'weight': 5, 'content': [{'end': 1378.009, 'text': "So another process that we'll now begin to focus on all the more this week is, invariably, this past week you ran up against some challenges.", 'start': 1370.962, 'duration': 7.047}, {'end': 1381.292, 'text': 'You probably created your very first bugs or mistakes in a program.', 'start': 1378.069, 'duration': 3.223}, {'end': 1384.655, 'text': "And so let's focus for a moment on actual techniques for debugging.", 'start': 1381.552, 'duration': 3.103}, {'end': 1388.278, 'text': 'As you spend more time this semester in the years to come.', 'start': 1385.195, 'duration': 3.083}, {'end': 1393.243, 'text': "if you continue to program, you're never, frankly, probably going to write bug-free code.", 'start': 1388.278, 'duration': 4.965}, {'end': 1397.525, 'text': 'Ultimately, your programs are just going to get more featureful, more sophisticated.', 'start': 1393.943, 'duration': 3.582}], 'summary': 'Focus on debugging techniques as you encounter challenges and begin to write more sophisticated code.', 'duration': 26.563, 'max_score': 1370.962, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE1370962.jpg'}, {'end': 1445.318, 'src': 'embed', 'start': 1422.955, 'weight': 6, 'content': [{'end': 1432.025, 'text': 'So what are some of the techniques and tools that folks use? Well, as an aside, a bug in a program is a mistake.', 'start': 1422.955, 'duration': 9.07}, {'end': 1433.507, 'text': "That's actually been around for some time.", 'start': 1432.045, 'duration': 1.462}, {'end': 1440.635, 'text': "If you've ever heard this tale, some 50-plus years ago in 1947, this is actually an entry in a log book.", 'start': 1433.947, 'duration': 6.688}, {'end': 1445.318, 'text': 'written by a famous computer scientist named Grace Hopper,', 'start': 1441.435, 'duration': 3.883}], 'summary': 'Techniques and tools used by folks, bug in a program is a mistake, entry in log book by grace hopper.', 'duration': 22.363, 'max_score': 1422.955, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE1422955.jpg'}, {'end': 1637.25, 'src': 'embed', 'start': 1595.142, 'weight': 0, 'content': [{'end': 1606.631, 'text': 'Let me go inside of this loop and just temporarily say something explicit like i is percent i backslash n, and then just plug in the value of i.', 'start': 1595.142, 'duration': 11.489}, {'end': 1608.432, 'text': 'This is not the program I want to write.', 'start': 1606.631, 'duration': 1.801}, {'end': 1615.119, 'text': "It's the program I'm temporarily writing, because now I'm going to go ahead and say make buggy dot slash buggy.", 'start': 1608.513, 'duration': 6.606}, {'end': 1619.163, 'text': 'And if I look now at the output, I have some helpful diagnostic information.', 'start': 1615.439, 'duration': 3.724}, {'end': 1620.964, 'text': 'i is 0, and I get a hash.', 'start': 1619.443, 'duration': 1.521}, {'end': 1622.984, 'text': 'i is 1, and I get a hash.', 'start': 1621.384, 'duration': 1.6}, {'end': 1623.685, 'text': '2, and I get a hash.', 'start': 1623.004, 'duration': 0.681}, {'end': 1624.425, 'text': '3, and I get a hash.', 'start': 1623.985, 'duration': 0.44}, {'end': 1625.185, 'text': 'OK, wait a minute.', 'start': 1624.545, 'duration': 0.64}, {'end': 1630.167, 'text': "I'm clearly going too many steps, because maybe I forgot that computers are essentially counting from 0.", 'start': 1625.525, 'duration': 4.642}, {'end': 1632.008, 'text': "And now, oh, it's less than or equal to.", 'start': 1630.167, 'duration': 1.841}, {'end': 1633.928, 'text': 'Now you see it.', 'start': 1632.488, 'duration': 1.44}, {'end': 1637.25, 'text': 'Again, trivial example, but just by using printf, you can see.', 'start': 1633.968, 'duration': 3.282}], 'summary': 'Debugging program to fix loop, showing i and output for each step.', 'duration': 42.108, 'max_score': 1595.142, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE1595142.jpg'}], 'start': 1352.504, 'title': 'Debugging techniques', 'summary': 'Explores debugging concepts, tools, and techniques, including print statements, debug50, and rubber duck debugging, emphasizing efficient bug resolution and historical anecdotes.', 'chapters': [{'end': 1481.759, 'start': 1352.504, 'title': 'Compilation and debugging techniques', 'summary': 'Discusses the concepts of compiling, debugging, and the inevitability of writing buggy code, emphasizing the use of tools and techniques for debugging, and also includes an interesting historical anecdote about the first computer bug.', 'duration': 129.255, 'highlights': ['The chapter discusses the concepts of compiling, debugging, and the inevitability of writing buggy code The chapter introduces the concepts of compiling and debugging, highlighting the inevitability of writing buggy code.', 'Emphasizing the use of tools and techniques for debugging The chapter emphasizes the use of tools and techniques for debugging, providing insights into real-world tools used by programmers to find faults in their code.', 'Includes an interesting historical anecdote about the first computer bug The chapter includes an interesting historical anecdote about the first computer bug, dating back to an entry in a log book in 1947 by Grace Hopper, a famous computer scientist.']}, {'end': 2169.639, 'start': 1481.759, 'title': 'Debugging techniques in programming', 'summary': 'Discusses common debugging techniques, such as using printf to diagnose logical errors, employing debug50 to step through code, and the rubber duck debugging method, to identify and solve programming bugs efficiently.', 'duration': 687.88, 'highlights': ['The chapter discusses common debugging techniques, such as using printf to diagnose logical errors The speaker demonstrates using printf to diagnose a logical error in the code where the program is intended to print three bricks but prints four instead.', "employing debug50 to step through code The speaker introduces debug50, a built-in debugger in VS Code, to walk through the code step by step, allowing for a more controlled and in-depth examination of the program's execution.", 'the rubber duck debugging method, to identify and solve programming bugs efficiently The chapter explains the concept of rubber duck debugging, where programmers talk through their code with an inanimate object, helping them identify logical errors and find solutions to their programming problems.']}, {'end': 2416.915, 'start': 2170.259, 'title': 'Debugging a program', 'summary': 'Discusses debugging techniques, including using print statements and the debugger to identify and resolve issues in a program, focusing on a specific function to fix logical errors in the code.', 'duration': 246.656, 'highlights': ['The program is attempting to get a negative integer input from the user using a function called get negative int, which currently does not exist in the CS50 library or elsewhere. The program attempts to use a non-existent function, get negative int, to retrieve a negative integer input from the user.', 'The function get negative int is declared and defined to return an integer and take no input. The function get negative int is declared and defined to return an integer and take no input.', 'A logical error is identified in the code, which is causing the program to behave incorrectly when attempting to get a negative integer input from the user. A logical error is identified that causes the program to behave incorrectly when getting a negative integer input from the user.', 'The debugging process involves using print statements (printf) and the debugger (debug50) to identify and resolve the issue within the get negative int function. The debugging process involves using print statements (printf) and the debugger (debug50) to identify and resolve the issue within the get negative int function.']}], 'duration': 1064.411, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE1352504.jpg', 'highlights': ['The chapter introduces the concepts of compiling and debugging, highlighting the inevitability of writing buggy code.', 'The chapter emphasizes the use of tools and techniques for debugging, providing insights into real-world tools used by programmers to find faults in their code.', 'The chapter includes an interesting historical anecdote about the first computer bug, dating back to an entry in a log book in 1947 by Grace Hopper, a famous computer scientist.', "The speaker introduces debug50, a built-in debugger in VS Code, to walk through the code step by step, allowing for a more controlled and in-depth examination of the program's execution.", 'The chapter explains the concept of rubber duck debugging, where programmers talk through their code with an inanimate object, helping them identify logical errors and find solutions to their programming problems.', 'A logical error is identified that causes the program to behave incorrectly when getting a negative integer input from the user.', 'The debugging process involves using print statements (printf) and the debugger (debug50) to identify and resolve the issue within the get negative int function.']}, {'end': 3330.649, 'segs': [{'end': 2447.055, 'src': 'embed', 'start': 2416.935, 'weight': 6, 'content': [{'end': 2419.916, 'text': "All right, so let's go ahead and do this.", 'start': 2416.935, 'duration': 2.981}, {'end': 2426.057, 'text': "We've got a bunch of possible approaches that we can take to solving some problem.", 'start': 2420.536, 'duration': 5.521}, {'end': 2427.518, 'text': "Let's go ahead and pace ourselves today, though.", 'start': 2426.097, 'duration': 1.421}, {'end': 2428.718, 'text': "Let's take a five minute break here.", 'start': 2427.538, 'duration': 1.18}, {'end': 2432.419, 'text': "And when we come back, we'll actually take a look at that computer's memory we've been talking about.", 'start': 2428.738, 'duration': 3.681}, {'end': 2433.299, 'text': 'See you in five.', 'start': 2432.799, 'duration': 0.5}, {'end': 2435.439, 'text': 'All right.', 'start': 2434.619, 'duration': 0.82}, {'end': 2438.58, 'text': "So let's.", 'start': 2437.78, 'duration': 0.8}, {'end': 2441.332, 'text': "Let's dive back in.", 'start': 2439.591, 'duration': 1.741}, {'end': 2447.055, 'text': 'And up until now, both by way of week one and problem set one.', 'start': 2441.712, 'duration': 5.343}], 'summary': 'Discussion covers possible problem-solving approaches and computer memory analysis. five-minute break included.', 'duration': 30.12, 'max_score': 2416.935, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE2416935.jpg'}, {'end': 2629.195, 'src': 'embed', 'start': 2602.141, 'weight': 2, 'content': [{'end': 2608.044, 'text': "And let's consider the fact that, even though we don't have to care exactly how this kind of thing is made,", 'start': 2602.141, 'duration': 5.903}, {'end': 2615.808, 'text': 'if this is like one gigabyte of memory for the sake of discussion, it stands to reason that if this thing is storing one billion bytes,', 'start': 2608.044, 'duration': 7.764}, {'end': 2618.83, 'text': 'one gigabyte then we can number them kind of arbitrarily.', 'start': 2615.808, 'duration': 3.022}, {'end': 2622.405, 'text': 'Like maybe this will be byte 0, 1, 2, 3, 4, 5, 6, 7, 8.', 'start': 2618.87, 'duration': 3.535}, {'end': 2626.094, 'text': 'And then maybe way down here in the bottom right corner is byte number 1 billion.', 'start': 2622.412, 'duration': 3.682}, {'end': 2629.195, 'text': 'We can just number these things, as might be our convention.', 'start': 2626.134, 'duration': 3.061}], 'summary': 'Discussion on storing one gigabyte of memory and numbering bytes arbitrarily.', 'duration': 27.054, 'max_score': 2602.141, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE2602141.jpg'}, {'end': 2844.241, 'src': 'heatmap', 'start': 2755.867, 'weight': 0.74, 'content': [{'end': 2764.294, 'text': "And I'm going to do score 1 plus score 2 plus score 3 divided by 3, close parenthesis, semicolon.", 'start': 2755.867, 'duration': 8.427}, {'end': 2768.217, 'text': 'So just some relatively simple arithmetic, just to compute the average of three scores,', 'start': 2764.314, 'duration': 3.903}, {'end': 2772, 'text': "if I'm curious what my average grade is in the class with these three assessments.", 'start': 2768.217, 'duration': 3.783}, {'end': 2774.882, 'text': 'All right, let me go ahead now and do make scores.', 'start': 2772.36, 'duration': 2.522}, {'end': 2777.44, 'text': 'Huh All right.', 'start': 2776.42, 'duration': 1.02}, {'end': 2780.022, 'text': "So I've somehow made an error already.", 'start': 2777.521, 'duration': 2.501}, {'end': 2787.745, 'text': "But this one is actually germane to a problem we hopefully won't encounter too frequently.", 'start': 2780.162, 'duration': 7.583}, {'end': 2792.527, 'text': "What's going on here? So underlined is score 1 plus score 2 plus score 3 divided by 3.", 'start': 2787.785, 'duration': 4.742}, {'end': 2795.888, 'text': 'Format specifies type double, but the argument has type int.', 'start': 2792.527, 'duration': 3.361}, {'end': 2801.431, 'text': "Well, what's going on here? Because the arithmetic seems to check out.", 'start': 2797.009, 'duration': 4.422}, {'end': 2805.422, 'text': 'Yeah Thank you.', 'start': 2801.471, 'duration': 3.951}, {'end': 2810.772, 'text': 'DAVID J.', 'start': 2810.572, 'duration': 0.2}, {'end': 2812.512, 'text': "Correct And we'll come back to this in more detail.", 'start': 2810.772, 'duration': 1.74}, {'end': 2817.114, 'text': "But indeed, what's happening here is I'm adding three ints together, obviously, because I defined them right up here.", 'start': 2812.572, 'duration': 4.542}, {'end': 2819.814, 'text': "And I'm dividing by another int, 3.", 'start': 2817.354, 'duration': 2.46}, {'end': 2824.635, 'text': 'But the catch is, recall that C, when it performs math, treats all of these things as integers.', 'start': 2819.814, 'duration': 4.821}, {'end': 2826.616, 'text': 'But integers are not floating point values.', 'start': 2824.755, 'duration': 1.861}, {'end': 2833.798, 'text': 'So if you actually want to get a precise average for your score without throwing away the remainder everything after the decimal point,', 'start': 2826.636, 'duration': 7.162}, {'end': 2835.578, 'text': "it turns out in this case we're going to have to.", 'start': 2833.798, 'duration': 1.78}, {'end': 2838.479, 'text': "We're going to have to.", 'start': 2835.598, 'duration': 2.881}, {'end': 2844.241, 'text': "We're going to have to convert this whole expression somehow to a float.", 'start': 2840.359, 'duration': 3.882}], 'summary': 'The transcript discusses computing the average of three scores, encountering an error due to integer division.', 'duration': 88.374, 'max_score': 2755.867, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE2755867.jpg'}, {'end': 2792.527, 'src': 'embed', 'start': 2764.314, 'weight': 7, 'content': [{'end': 2768.217, 'text': 'So just some relatively simple arithmetic, just to compute the average of three scores,', 'start': 2764.314, 'duration': 3.903}, {'end': 2772, 'text': "if I'm curious what my average grade is in the class with these three assessments.", 'start': 2768.217, 'duration': 3.783}, {'end': 2774.882, 'text': 'All right, let me go ahead now and do make scores.', 'start': 2772.36, 'duration': 2.522}, {'end': 2777.44, 'text': 'Huh All right.', 'start': 2776.42, 'duration': 1.02}, {'end': 2780.022, 'text': "So I've somehow made an error already.", 'start': 2777.521, 'duration': 2.501}, {'end': 2787.745, 'text': "But this one is actually germane to a problem we hopefully won't encounter too frequently.", 'start': 2780.162, 'duration': 7.583}, {'end': 2792.527, 'text': "What's going on here? So underlined is score 1 plus score 2 plus score 3 divided by 3.", 'start': 2787.785, 'duration': 4.742}], 'summary': 'Compute the average of three scores for grade calculation.', 'duration': 28.213, 'max_score': 2764.314, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE2764314.jpg'}, {'end': 3027.681, 'src': 'embed', 'start': 2989.747, 'weight': 0, 'content': [{'end': 2993.03, 'text': "And so let's take a look back at this memory here to see what these things might look like in memory.", 'start': 2989.747, 'duration': 3.283}, {'end': 2994.411, 'text': "Here's that grid of memory.", 'start': 2993.35, 'duration': 1.061}, {'end': 2996.714, 'text': 'And each of these, recall, represents a byte.', 'start': 2994.912, 'duration': 1.802}, {'end': 3004.868, 'text': 'So just to be clear, if I store score 1 in memory first, how many bytes will it take up? So 4, a.k.a.', 'start': 2997.074, 'duration': 7.794}, {'end': 3005.328, 'text': '32 bits.', 'start': 3005.048, 'duration': 0.28}, {'end': 3009.551, 'text': 'So I might draw score 1 as filling up this part of the memory.', 'start': 3005.388, 'duration': 4.163}, {'end': 3012.592, 'text': "It's really up to the computer as to whether it goes here or down there or wherever.", 'start': 3009.591, 'duration': 3.001}, {'end': 3015.974, 'text': "I'm just keeping the pictures clean, though, for today, from the top left on down.", 'start': 3012.832, 'duration': 3.142}, {'end': 3021.497, 'text': 'If I then declare another variable called score 2, it might end up over there, also taking up 4 bytes.', 'start': 3016.394, 'duration': 5.103}, {'end': 3023.739, 'text': 'And then score 3 might end up here.', 'start': 3021.537, 'duration': 2.202}, {'end': 3027.681, 'text': "And so that's just representing what's going on inside of the computer's memory.", 'start': 3024.159, 'duration': 3.522}], 'summary': 'Memory grid represents bytes, each score takes 4 bytes.', 'duration': 37.934, 'max_score': 2989.747, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE2989747.jpg'}, {'end': 3298.952, 'src': 'embed', 'start': 3269.859, 'weight': 5, 'content': [{'end': 3272.722, 'text': "Now, this program's still not really solving all the problems we described.", 'start': 3269.859, 'duration': 2.863}, {'end': 3276.386, 'text': "Like, I still can only store three scores, but we'll come back to something like that before long.", 'start': 3272.742, 'duration': 3.644}, {'end': 3285.115, 'text': "But for now, we're just introducing a new syntax and a new feature whereby I can now store multiple values in the same variable.", 'start': 3276.926, 'duration': 8.189}, {'end': 3287.983, 'text': "Well, let's enhance this a bit more.", 'start': 3286.442, 'duration': 1.541}, {'end': 3295.189, 'text': "Instead of hard coding these scores, as was identified as a problem, let's go ahead and use getInt to ask the user for a score.", 'start': 3288.043, 'duration': 7.146}, {'end': 3298.952, 'text': "Let's then use getInt to ask the user for another score.", 'start': 3295.89, 'duration': 3.062}], 'summary': 'Introducing a new syntax to store multiple values in the same variable, with plans to address limitations and enhance functionality.', 'duration': 29.093, 'max_score': 3269.859, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE3269859.jpg'}], 'start': 2416.935, 'title': 'C data types, program design, and arrays', 'summary': 'Covers c data types and memory organization, including sizes of bools, chars, ints, floats, longs, and doubles. it also introduces a program in c for averaging exam scores and discusses the concept of arrays in c for storing multiple values contiguously in memory.', 'chapters': [{'end': 2697.422, 'start': 2416.935, 'title': 'C data types and memory', 'summary': 'Introduces c data types, their sizes, and memory organization, highlighting the sizes of different data types, such as bools, chars, ints, floats, longs, and doubles, and explaining how memory is organized and used to store different data types.', 'duration': 280.487, 'highlights': ["The size of data types in C varies, with a bool using 1 byte, a char using 1 byte, an int using 4 bytes, a float using 4 bytes, a long and a double using 8 bytes each, and a string's space usage being variable.", 'Computers store bool values using one byte, although strictly speaking, only one bit is needed, resulting in some inefficiency.', "ASCII, which uses one byte, was originally limited to only 256 maximally possible characters due to char's size being one byte.", 'Memory organization is depicted as a grid, with different data types occupying varying numbers of contiguous bytes, and is abstracted as a canvas for painting different types of data, all represented ultimately as 0s and 1s.']}, {'end': 2972.45, 'start': 2697.422, 'title': 'Designing a program for averaging scores', 'summary': 'Introduces a program in c to average three exam scores, highlighting the need to convert integer values to floating point for accurate results, the limitations of hardcoding scores, and the potential issues with scalability and reusability.', 'duration': 275.028, 'highlights': ['The need to convert integer values to floating point for accurate results in the program, as demonstrated by the error in the initial implementation.', 'The limitation of hardcoding scores in the program, preventing the reusability and scalability of the solution for handling more than three scores.', "The potential issues with scalability and reusability due to the program's design, as it is limited to processing only three scores and lacks flexibility for handling a larger dataset."]}, {'end': 3330.649, 'start': 2972.452, 'title': 'Storing multiple values in memory using arrays', 'summary': 'Discusses the concept of arrays in programming languages like c, which allows the user to store multiple values of the same type contiguously in memory using a single variable, demonstrating the syntax and zero-indexing approach, ultimately solving the problem of declaring multiple variables for each value.', 'duration': 358.197, 'highlights': ['Arrays allow storing multiple values of the same type using a single variable, solving the problem of declaring multiple variables for each value. The concept of arrays in programming languages like C allows the user to store multiple values of the same type contiguously in memory using a single variable, thus solving the problem of declaring multiple variables for each value.', 'Demonstrates the syntax and zero-indexing approach while accessing array elements. The chapter demonstrates the syntax of declaring an array and accessing its elements using zero-indexing, which requires starting counting at 0 and shows that arrays in C are 0 indexed.', 'The chapter discusses using getInt to dynamically store user input in array elements. The discussion involves using getInt to dynamically store user input in array elements, allowing for a more dynamic and flexible approach to storing values in memory.']}], 'duration': 913.714, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE2416935.jpg', 'highlights': ['Arrays in C store multiple values contiguously in memory using a single variable.', 'The size of data types in C varies, with a bool using 1 byte, a char using 1 byte, an int using 4 bytes, a float using 4 bytes, a long and a double using 8 bytes each.', 'Computers store bool values using one byte, although strictly speaking, only one bit is needed.', 'Memory organization is depicted as a grid, with different data types occupying varying numbers of contiguous bytes.', 'The need to convert integer values to floating point for accurate results in the program.', 'The limitation of hardcoding scores in the program, preventing reusability and scalability.', 'Demonstrates the syntax and zero-indexing approach while accessing array elements.', "The potential issues with scalability and reusability due to the program's design."]}, {'end': 4349.116, 'segs': [{'end': 3412.568, 'src': 'embed', 'start': 3347.057, 'weight': 2, 'content': [{'end': 3351.601, 'text': "But now I've kind of introduced another sort of symptom of bad programming.", 'start': 3347.057, 'duration': 4.544}, {'end': 3356.764, 'text': "There's this expression in programming, too, called code smell, where something smells a little off.", 'start': 3351.641, 'duration': 5.123}, {'end': 3361.307, 'text': "And there's something off here in that I could do better with this code here.", 'start': 3356.844, 'duration': 4.463}, {'end': 3368.572, 'text': 'Does anyone see an opportunity to improve the design of this code here, if my goal still is just to get three scores from the user,', 'start': 3361.487, 'duration': 7.085}, {'end': 3371.694, 'text': 'but without it smelling kind of bad? Yeah.', 'start': 3368.572, 'duration': 3.122}, {'end': 3373.575, 'text': 'You can use a for loop.', 'start': 3371.954, 'duration': 1.621}, {'end': 3377.516, 'text': 'That way, you can inhabit it without blocking DAVID J.', 'start': 3373.595, 'duration': 3.921}, {'end': 3378.057, 'text': 'Yeah, exactly.', 'start': 3377.516, 'duration': 0.541}, {'end': 3380.178, 'text': 'Those lines of code are almost identical.', 'start': 3378.097, 'duration': 2.081}, {'end': 3383.979, 'text': "And honestly, the only thing that's changing is the number, and it's just incrementing by one.", 'start': 3380.278, 'duration': 3.701}, {'end': 3386.1, 'text': 'We have all of the building blocks to do this better.', 'start': 3383.999, 'duration': 2.101}, {'end': 3387.841, 'text': 'So let me go ahead and improve this.', 'start': 3386.16, 'duration': 1.681}, {'end': 3389.682, 'text': 'Let me go ahead and delete that code.', 'start': 3387.961, 'duration': 1.721}, {'end': 3391.963, 'text': 'Let me go ahead now and have a for loop.', 'start': 3390.462, 'duration': 1.501}, {'end': 3396.83, 'text': 'So for int i gets 0, i less than 3, i plus plus.', 'start': 3392.603, 'duration': 4.227}, {'end': 3405.903, 'text': 'Then inside of this for loop, I can distill all three of those lines into something more generic, like scores bracket i equals get int.', 'start': 3397.21, 'duration': 8.693}, {'end': 3407.866, 'text': 'And now ask the user just once.', 'start': 3405.983, 'duration': 1.883}, {'end': 3409.867, 'text': 'by a get int for a score.', 'start': 3408.407, 'duration': 1.46}, {'end': 3412.568, 'text': 'So this is where arrays start to get pretty powerful.', 'start': 3410.188, 'duration': 2.38}], 'summary': 'Identifying code smell and improving code design using a for loop to handle three scores more efficiently.', 'duration': 65.511, 'max_score': 3347.057, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE3347057.jpg'}, {'end': 3921.725, 'src': 'embed', 'start': 3894.375, 'weight': 0, 'content': [{'end': 3897.156, 'text': 'All right, let me go ahead and do this now the week one way.', 'start': 3894.375, 'duration': 2.781}, {'end': 3898.237, 'text': 'This was kind of stupid.', 'start': 3897.316, 'duration': 0.921}, {'end': 3900.637, 'text': "Let's just do printf quote unquote.", 'start': 3898.317, 'duration': 2.32}, {'end': 3902.058, 'text': "Actually, let's do this.", 'start': 3901.458, 'duration': 0.6}, {'end': 3905.239, 'text': 'String s equals quote unquote hi.', 'start': 3902.278, 'duration': 2.961}, {'end': 3908.961, 'text': "And then let's go ahead and do a simple printf with percent s.", 'start': 3905.779, 'duration': 3.182}, {'end': 3910.341, 'text': 'Printing out s is there.', 'start': 3908.961, 'duration': 1.38}, {'end': 3913.122, 'text': "So now I've rewound to last week where we began this story.", 'start': 3910.601, 'duration': 2.521}, {'end': 3917.944, 'text': "But you'll notice that if we keep playing around with this, whoops.", 'start': 3913.642, 'duration': 4.302}, {'end': 3921.725, 'text': 'What did I do here? Oh, let me introduce the CS50 library here.', 'start': 3919.064, 'duration': 2.661}], 'summary': 'The transcript involves coding exercises with printf and string manipulation.', 'duration': 27.35, 'max_score': 3894.375, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE3894375.jpg'}], 'start': 3330.709, 'title': 'Improving code design with arrays and loops, working with arrays and characters, and understanding strings and memory in programming', 'summary': 'Covers the improvement of code design through arrays and loops, demonstrating dynamic acquisition of multiple scores, user input for number of scores in programming. it also discusses creating arrays, using characters for strings, and the implications of string length on memory storage in programming.', 'chapters': [{'end': 3639.472, 'start': 3330.709, 'title': 'Improving code design with arrays and loops', 'summary': 'Discusses the improvement of code design through the use of arrays and loops, demonstrating the dynamic acquisition of multiple scores and the introduction of user input for the number of scores, ultimately resulting in a better-designed program.', 'duration': 308.763, 'highlights': ["The program dynamically acquires three different scores and puts them in three different locations, resulting in a better-designed program. The program demonstrates the use of arrays and loops to dynamically acquire three different scores and store them in three different locations, which improves the program's design.", "Introduction of user input for the number of scores, enabling the program to be dynamic and adaptable to the user's discretion. The introduction of user input for the number of scores allows the program to be dynamic and adaptable, as the user can specify the number of scores, improving the program's flexibility.", "Explanation of the purpose and benefits of using arrays to store multiple scores, reducing the need for multiple variable names and enabling the use of different data types. The explanation of using arrays to store multiple scores reduces the need for multiple variable names and allows the use of different data types, ultimately optimizing the program's design and memory usage."]}, {'end': 3893.955, 'start': 3640.172, 'title': 'Working with arrays and characters in c', 'summary': 'Discusses the creation of arrays to store multiple values and the use of characters to represent strings, demonstrating the implicit type conversion of characters to integers in c programming.', 'duration': 253.783, 'highlights': ['The chapter discusses the creation of arrays to store multiple values, emphasizing the ability to use arrays to store characters, which occupy less space than integers.', 'It demonstrates the process of using multiple variables to store characters and printing them sequentially, highlighting the inefficiency and impracticality of this approach.', 'The chapter shows the implicit type conversion of characters to integers in C programming, using the ASCII values of the characters as an example and highlighting the ability to explicitly convert data types using typecasting.']}, {'end': 4349.116, 'start': 3894.375, 'title': 'Understanding strings and memory in programming', 'summary': 'Discusses the implementation of strings as arrays of characters, the use of null character as a delimiter, and the implications of string length on memory storage, emphasizing the dynamic nature of string length in memory.', 'duration': 454.741, 'highlights': ['Strings implemented as arrays of characters The chapter explains that strings are implemented as arrays of characters, introducing the concept of accessing individual characters and the implications of this implementation on memory.', 'Use of null character as a delimiter The discussion highlights the use of null character as a special symbol to delineate the end of a string, with a clear explanation of its representation in memory and its role in distinguishing one string from another.', 'Implications of dynamic string length on memory storage The chapter explores the implications of dynamic string length on memory storage, emphasizing the need to distinguish one string from another and the variability of string length compared to other data types.']}], 'duration': 1018.407, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE3330709.jpg', 'highlights': ['The program dynamically acquires three different scores and puts them in three different locations, resulting in a better-designed program.', "Introduction of user input for the number of scores, enabling the program to be dynamic and adaptable to the user's discretion.", 'Explanation of the purpose and benefits of using arrays to store multiple scores, reducing the need for multiple variable names and enabling the use of different data types.', 'The chapter discusses the creation of arrays to store multiple values, emphasizing the ability to use arrays to store characters, which occupy less space than integers.', 'Strings implemented as arrays of characters The chapter explains that strings are implemented as arrays of characters, introducing the concept of accessing individual characters and the implications of this implementation on memory.', 'Use of null character as a delimiter The discussion highlights the use of null character as a special symbol to delineate the end of a string, with a clear explanation of its representation in memory and its role in distinguishing one string from another.']}, {'end': 5243.651, 'segs': [{'end': 4678.138, 'src': 'embed', 'start': 4637.702, 'weight': 0, 'content': [{'end': 4638.943, 'text': "So that's a topic we'll come back to.", 'start': 4637.702, 'duration': 1.241}, {'end': 4640.564, 'text': 'But it was generally for efficiency.', 'start': 4639.003, 'duration': 1.561}, {'end': 4642.105, 'text': 'And other question.', 'start': 4640.584, 'duration': 1.521}, {'end': 4649.391, 'text': 'Yeah Why not store all characters DAVID J.', 'start': 4642.125, 'duration': 7.266}, {'end': 4649.771, 'text': 'Good question.', 'start': 4649.391, 'duration': 0.38}, {'end': 4652.226, 'text': 'Why not store the? OK, same one.', 'start': 4649.791, 'duration': 2.435}, {'end': 4664.196, 'text': "Why not store the null character at the beginning? You could, let's see, why not store it at the beginning? You could do that.", 'start': 4652.586, 'duration': 11.61}, {'end': 4678.138, 'text': 'You could absolutely, well, could you do this? If you were to do that at the beginning, Short answer, no.', 'start': 4665.997, 'duration': 12.141}], 'summary': 'Discussing storing characters for efficiency, considering null character placement.', 'duration': 40.436, 'max_score': 4637.702, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE4637702.jpg'}, {'end': 4906.516, 'src': 'embed', 'start': 4876.565, 'weight': 1, 'content': [{'end': 4877.866, 'text': 'Fast forward to the end of the story.', 'start': 4876.565, 'duration': 1.301}, {'end': 4886.789, 'text': 'Once I get to the end of the string, technically one space past the end of the string, name bracket i will equal backslash 0.', 'start': 4878.206, 'duration': 8.583}, {'end': 4888.149, 'text': "So I don't increment i anymore.", 'start': 4886.789, 'duration': 1.36}, {'end': 4890.45, 'text': 'I end up just printing the result.', 'start': 4888.169, 'duration': 2.281}, {'end': 4894.872, 'text': 'So what we seem to have here, with some low level C code, just this,', 'start': 4890.97, 'duration': 3.902}, {'end': 4899.793, 'text': "while loop is a program that figures out the length of a given string that's been typed in.", 'start': 4894.872, 'duration': 4.921}, {'end': 4903.935, 'text': "Let's practice our abstraction and decompose this into maybe a helper function here.", 'start': 4900.134, 'duration': 3.801}, {'end': 4906.516, 'text': 'Let me actually grab all of this code here.', 'start': 4904.275, 'duration': 2.241}], 'summary': 'Low level c code uses a while loop to find string length.', 'duration': 29.951, 'max_score': 4876.565, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE4876565.jpg'}, {'end': 5069.795, 'src': 'heatmap', 'start': 4907.176, 'weight': 0.737, 'content': [{'end': 4914.279, 'text': 'And let me assume for the sake of discussion for a moment that I can just call a function now called string length.', 'start': 4907.176, 'duration': 7.103}, {'end': 4917.501, 'text': 'And the length of the string is name that I want to get.', 'start': 4914.88, 'duration': 2.621}, {'end': 4923.125, 'text': "And then I'll go ahead and print out, just as before, with percent i, the length of that string.", 'start': 4917.882, 'duration': 5.243}, {'end': 4926.407, 'text': "So now I'm abstracting away this notion of figuring out the length of a string.", 'start': 4923.325, 'duration': 3.082}, {'end': 4929.128, 'text': "That's an opportunity for me to create my own function.", 'start': 4926.787, 'duration': 2.341}, {'end': 4935.988, 'text': "If I want to create a function called string length, I'll claim that I want to take a string as input.", 'start': 4929.588, 'duration': 6.4}, {'end': 4949.911, 'text': 'And what should I have this function return as its return type? What should get string presumably return? Yeah? And int makes sense.', 'start': 4936.789, 'duration': 13.122}, {'end': 4955.853, 'text': "Float really wouldn't make sense, because we're measuring things that are integers, in this case, the length of something.", 'start': 4949.971, 'duration': 5.882}, {'end': 4957.334, 'text': "So indeed, let's have it return an int.", 'start': 4955.893, 'duration': 1.441}, {'end': 4959.815, 'text': 'I can pretty much use the same code as before.', 'start': 4957.694, 'duration': 2.121}, {'end': 4962.696, 'text': "So I'm just going to paste what I cut earlier in the file.", 'start': 4959.835, 'duration': 2.861}, {'end': 4965.898, 'text': 'And the only thing I have to change here is the name.', 'start': 4963.136, 'duration': 2.762}, {'end': 4973.68, 'text': "of the variable, because now this function, I decided kind of arbitrarily that I'm going to call it s, just to be more generic.", 'start': 4966.678, 'duration': 7.002}, {'end': 4976.921, 'text': "So I'm going to look at s bracket i at each location.", 'start': 4974.161, 'duration': 2.76}, {'end': 4978.262, 'text': "And I don't want to print it at the end.", 'start': 4977.001, 'duration': 1.261}, {'end': 4979.382, 'text': 'This would be a side effect.', 'start': 4978.302, 'duration': 1.08}, {'end': 4989.826, 'text': "What's the line of code I should include here if I actually want to hand back the total length? Yeah? Say again? return i in this case.", 'start': 4979.942, 'duration': 9.884}, {'end': 4991.467, 'text': "So I'm going to go ahead and return.", 'start': 4990.166, 'duration': 1.301}, {'end': 4999.373, 'text': 'i not print it because now my main function can use the return value stored in length and print it on the next line itself.', 'start': 4991.467, 'duration': 7.906}, {'end': 5000.474, 'text': 'I just need a prototype.', 'start': 4999.493, 'duration': 0.981}, {'end': 5003.156, 'text': "So that's my one forgivable copy paste here.", 'start': 5000.554, 'duration': 2.602}, {'end': 5004.898, 'text': "I'm going to rerun make length.", 'start': 5003.597, 'duration': 1.301}, {'end': 5006.038, 'text': "Hopefully I didn't screw up.", 'start': 5005.138, 'duration': 0.9}, {'end': 5007.059, 'text': "I didn't.", 'start': 5006.699, 'duration': 0.36}, {'end': 5008.48, 'text': 'Dot slash length.', 'start': 5007.36, 'duration': 1.12}, {'end': 5009.882, 'text': "I'll type in hi.", 'start': 5009.001, 'duration': 0.881}, {'end': 5011.463, 'text': "Whoops I'll type in hi again.", 'start': 5009.922, 'duration': 1.541}, {'end': 5012.784, 'text': 'That works.', 'start': 5012.364, 'duration': 0.42}, {'end': 5015.166, 'text': "I'll type in bye again, and so forth.", 'start': 5012.804, 'duration': 2.362}, {'end': 5019.402, 'text': 'All right, so now we have a function that determines the length of a string.', 'start': 5015.779, 'duration': 3.623}, {'end': 5021.985, 'text': "Well, it turns out we didn't actually need this all along.", 'start': 5019.763, 'duration': 2.222}, {'end': 5026.709, 'text': 'It turns out that we can get rid of my own custom string length function here.', 'start': 5022.085, 'duration': 4.624}, {'end': 5034.256, 'text': 'I can definitely delete the whole implementation down here, because it turns out in a file called string.h, which is a new header file.', 'start': 5027.129, 'duration': 7.127}, {'end': 5038.5, 'text': 'today we actually have access to a function called, more succinctly, strlen.', 'start': 5034.256, 'duration': 4.244}, {'end': 5041.902, 'text': 'S-T-R-L-E-N, which literally does that.', 'start': 5039, 'duration': 2.902}, {'end': 5050.106, 'text': 'This is a function that comes with C, albeit in the string.h header file, and it does pretty much what we just implemented manually.', 'start': 5042.122, 'duration': 7.984}, {'end': 5054.148, 'text': "So here's an example of, admittedly, a wheel we just reinvented, but no more.", 'start': 5050.466, 'duration': 3.682}, {'end': 5055.209, 'text': "We don't have to do that.", 'start': 5054.308, 'duration': 0.901}, {'end': 5057.71, 'text': 'And how do you know what kinds of functions exist?', 'start': 5055.509, 'duration': 2.201}, {'end': 5065.493, 'text': "Well, let me actually pop out of my browser here to a website that is a CS50's incarnation of what are called manual pages.", 'start': 5057.73, 'duration': 7.763}, {'end': 5069.795, 'text': 'It turns out that in a lot of systems Macs and Unix and Linux systems,', 'start': 5065.873, 'duration': 3.922}], 'summary': 'Creating and optimizing a string length function in c, only to later discover a built-in function called strlen in the string.h header file.', 'duration': 162.619, 'max_score': 4907.176, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE4907176.jpg'}], 'start': 4349.196, 'title': 'Memory representation and manipulation of strings in c', 'summary': 'Discusses the memory representation of strings, dynamic memory allocation, use of null value, and standardization of string lengths. it also demonstrates determining string length, abstracting it into a function, introducing strlen function, and accessing manual pages for c functions.', 'chapters': [{'end': 4711.651, 'start': 4349.196, 'title': 'Memory representation of strings', 'summary': 'Discusses the underlying representation of strings, dynamic memory allocation for strings, the use of null value to distinguish the end of a string, and the standardization of string lengths in memory for efficiency.', 'duration': 362.455, 'highlights': ['The chapter discusses the underlying representation of strings, dynamic memory allocation for strings, and the use of null value to distinguish the end of a string. The discussion provides insight into the fundamental representation of strings and the dynamic memory allocation technique, crucial for understanding the implementation of cryptography and encryption.', 'The use of null value to distinguish the end of a string is explained, highlighting the necessity of a byte to solve this problem. The explanation emphasizes the minimalistic approach of using one byte to distinguish the end of one string from the start of another, crucial for reliable memory distinction.', 'The standardization of string lengths in memory for efficiency is discussed, highlighting the benefits in terms of memory usage and performance increases. The discussion delves into the efficiency and performance gains achieved through standardizing the size of data types in memory, providing insights into the reasons behind this approach.']}, {'end': 5243.651, 'start': 4711.931, 'title': 'Manipulating strings in c', 'summary': 'Demonstrates how to determine the length of a string in c using low-level code and then abstracting it into a function; it also introduces the strlen function from string.h and highlights the accessibility of manual pages for c functions.', 'duration': 531.72, 'highlights': ['The chapter demonstrates how to determine the length of a string in C using low-level code and then abstracting it into a function, which allows for the creation of a custom function to calculate the length of a string, with examples showing the functioning of the code.', 'It introduces the strlen function from string.h, which is a built-in function in C that calculates the length of a string, and discusses the availability of manual pages for C functions like strlen, providing documentation on the usage and syntax of the function.', "The chapter highlights the accessibility of manual pages for C functions, particularly the CS50's version of manual pages that present a beginner-friendly format, making it easier to understand and utilize functions such as strlen for manipulating strings in C."]}], 'duration': 894.455, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE4349196.jpg', 'highlights': ['The standardization of string lengths in memory for efficiency is discussed, highlighting the benefits in terms of memory usage and performance increases.', 'The chapter discusses the underlying representation of strings, dynamic memory allocation for strings, and the use of null value to distinguish the end of a string.', 'The chapter demonstrates how to determine the length of a string in C using low-level code and then abstracting it into a function, which allows for the creation of a custom function to calculate the length of a string.']}, {'end': 5666.143, 'segs': [{'end': 5419.682, 'src': 'embed', 'start': 5389.223, 'weight': 0, 'content': [{'end': 5391.444, 'text': 'Let me go ahead and include cs50.h.', 'start': 5389.223, 'duration': 2.221}, {'end': 5397.728, 'text': 'Let me include standardio.h and this new thing, string.h as well at the top.', 'start': 5391.925, 'duration': 5.803}, {'end': 5400.229, 'text': "I'm going to do the usual int main void here.", 'start': 5398.288, 'duration': 1.941}, {'end': 5406.053, 'text': "And then in this program, suppose for the sake of discussion that I didn't know about %s for printf.", 'start': 5400.63, 'duration': 5.423}, {'end': 5409.956, 'text': 'Or heck, maybe early on there was no %s format code.', 'start': 5406.133, 'duration': 3.823}, {'end': 5413.018, 'text': 'And so there was no easy way to print strings.', 'start': 5410.236, 'duration': 2.782}, {'end': 5419.682, 'text': 'Well, at least if we know that strings are just arrays of characters, we could use %c as a workaround, so to speak,', 'start': 5413.358, 'duration': 6.324}], 'summary': 'The program demonstrates the use of different header files and the workaround for printing strings using %c as there was no %s format code available initially.', 'duration': 30.459, 'max_score': 5389.223, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE5389223.jpg'}, {'end': 5580.514, 'src': 'embed', 'start': 5549.192, 'weight': 2, 'content': [{'end': 5554.073, 'text': "Now, it is well designed in that I'm using someone else's library function.", 'start': 5549.192, 'duration': 4.881}, {'end': 5555.373, 'text': "Like, I've not reinvented a wheel.", 'start': 5554.093, 'duration': 1.28}, {'end': 5557.053, 'text': "There's no line 15 or below.", 'start': 5555.413, 'duration': 1.64}, {'end': 5558.914, 'text': "I didn't implement string length myself.", 'start': 5557.074, 'duration': 1.84}, {'end': 5562.655, 'text': "So I'm at least kind of practicing what I've preached.", 'start': 5559.554, 'duration': 3.101}, {'end': 5568.936, 'text': "But there's still an imperfection, a sub-optimality.", 'start': 5564.735, 'duration': 4.201}, {'end': 5570.757, 'text': "This one's really subtle, though.", 'start': 5569.256, 'duration': 1.501}, {'end': 5574.219, 'text': 'And you have to think about how loops work.', 'start': 5571.874, 'duration': 2.345}, {'end': 5580.514, 'text': "What am I doing that's not super efficient? Yeah, in back.", 'start': 5575.322, 'duration': 5.192}], 'summary': 'Using existing library functions, avoiding reinventing the wheel, but facing sub-optimality due to subtle inefficiencies in loops.', 'duration': 31.322, 'max_score': 5549.192, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE5549192.jpg'}], 'start': 5244.391, 'title': 'Representation techniques and library functions in c', 'summary': 'Discusses ascii representation, storage of characters and strings, integer overflow, floating point imprecision, and explores library functions in c programming, highlighting potential inefficiency using strlen multiple times in a loop.', 'chapters': [{'end': 5365.726, 'start': 5244.391, 'title': 'Representation techniques and ascii', 'summary': 'Discusses representation of characters and strings in a computer, including ascii representation of characters, storage of spaces, null termination of strings, and challenges with integer overflow and floating point imprecision in scientific and financial computing.', 'duration': 121.335, 'highlights': ['Computers store spaces as the decimal number 32 or a pattern of 0s and 1s, and all US English keys on a keyboard can be represented with a number, including emojis and other languages.', 'Strings are accompanied by nulls at the end, as other data types have well-defined finite length, such as one byte for char and four bytes for ints.', 'Challenges like integer overflow and floating point imprecision are addressed in scientific and financial computing through libraries that manage memory allocation for higher precision values, using sequences of bytes and remembering their length.']}, {'end': 5666.143, 'start': 5367.502, 'title': 'Library functions in c programming', 'summary': 'Explores the use of library functions in c programming, focusing on the string.h library function and the potential inefficiency when using strlen multiple times in a loop.', 'duration': 298.641, 'highlights': ['The chapter explores the use of library functions in C programming The chapter introduces the use of various library functions in C programming, such as the string.h library function, to demonstrate the practical application of these functions.', 'The potential inefficiency when using strlen multiple times in a loop The chapter highlights the inefficiency of calling the strlen function multiple times within a loop, as it repeatedly calculates the length of the string, resulting in suboptimal performance and suggests optimizing the code by storing the length in a variable before entering the loop.']}], 'duration': 421.752, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE5244391.jpg', 'highlights': ['Computers store spaces as the decimal number 32 or a pattern of 0s and 1s, representing all US English keys, including emojis and other languages.', 'Strings are accompanied by nulls at the end, with well-defined finite lengths for different data types, such as one byte for char and four bytes for ints.', 'Challenges like integer overflow and floating point imprecision are addressed through libraries managing memory allocation for higher precision values.']}, {'end': 6375.98, 'segs': [{'end': 5691.238, 'src': 'embed', 'start': 5666.183, 'weight': 3, 'content': [{'end': 5672.832, 'text': "Yeah, back there? So store it in a variable, right? That's been our answer most any time we want to keep something around.", 'start': 5666.183, 'duration': 6.649}, {'end': 5678.954, 'text': 'So how could I do this? Well, I could do something like this, int maybe length equals strlen of s.', 'start': 5672.892, 'duration': 6.062}, {'end': 5681.875, 'text': 'Then I can just change this function call, so to speak.', 'start': 5678.954, 'duration': 2.921}, {'end': 5683.616, 'text': 'And let me refix my spelling here.', 'start': 5681.935, 'duration': 1.681}, {'end': 5686.757, 'text': 'Let me fix this to be now comparing against length.', 'start': 5684.136, 'duration': 2.621}, {'end': 5691.238, 'text': 'And this is now OK, because now strlen is only called once on line 9.', 'start': 5686.997, 'duration': 4.241}], 'summary': 'Storing in a variable reduces strlen function calls, improving efficiency.', 'duration': 25.055, 'max_score': 5666.183, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE5666183.jpg'}, {'end': 5792.933, 'src': 'embed', 'start': 5742.651, 'weight': 0, 'content': [{'end': 5752.435, 'text': 'Let me go ahead and write a quick program here that maybe capitalizes the beginning of the changes to uppercase, some string that the user types in.', 'start': 5742.651, 'duration': 9.784}, {'end': 5755.437, 'text': 'So let me go ahead and code a file called uppercase.c.', 'start': 5752.796, 'duration': 2.641}, {'end': 5759.919, 'text': "Up here, I'll use my new friends, cs50.h and stdio and string.h, so stdio.", 'start': 5756.477, 'duration': 3.442}, {'end': 5767.703, 'text': 'And string.h, so just as before, int main void.', 'start': 5764.381, 'duration': 3.322}, {'end': 5776.328, 'text': "And then inside of main, what I'm going to do this time is let's ask the user for a string s using get string, asking them for the before value.", 'start': 5768.203, 'duration': 8.125}, {'end': 5779.349, 'text': 'And then let me go ahead and just print out something like after.', 'start': 5777.128, 'duration': 2.221}, {'end': 5784.891, 'text': 'so that it just so I can see what the uppercase version thereof is.', 'start': 5781.13, 'duration': 3.761}, {'end': 5787.872, 'text': 'And then after this, let me go ahead and do the following.', 'start': 5785.551, 'duration': 2.321}, {'end': 5792.933, 'text': "For int i equals 0, let's practice that same lesson.", 'start': 5788.052, 'duration': 4.881}], 'summary': 'Writing a program to capitalize user input in c using cs50.h and stdio with string.h', 'duration': 50.282, 'max_score': 5742.651, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE5742651.jpg'}, {'end': 5840.6, 'src': 'embed', 'start': 5816.475, 'weight': 6, 'content': [{'end': 5824.706, 'text': 'Well, how can I go about doing this? Well, you might recall that there is this ASCII chart.', 'start': 5816.475, 'duration': 8.231}, {'end': 5826.348, 'text': "So let's just consult this real quick.", 'start': 5824.766, 'duration': 1.582}, {'end': 5829.25, 'text': "On the ASCIIchart.com, we've looked at this last week.", 'start': 5826.888, 'duration': 2.362}, {'end': 5832.533, 'text': 'Notice that A, capital A, is 65.', 'start': 5829.51, 'duration': 3.023}, {'end': 5834.014, 'text': 'Capital B is 66.', 'start': 5832.533, 'duration': 1.481}, {'end': 5835.416, 'text': 'Capital C is 67.', 'start': 5834.014, 'duration': 1.402}, {'end': 5838.799, 'text': "And heck, here's lowercase a, lowercase b, lowercase c.", 'start': 5835.416, 'duration': 3.383}, {'end': 5840.6, 'text': "And that's 97, 98, 99.", 'start': 5838.799, 'duration': 1.801}], 'summary': 'Using the ascii chart, a=65, b=66, c=67, a=97, b=98, c=99.', 'duration': 24.125, 'max_score': 5816.475, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE5816475.jpg'}, {'end': 6094.101, 'src': 'embed', 'start': 6067.471, 'weight': 1, 'content': [{'end': 6072.256, 'text': 'It apparently takes a char as input and returns an int, which is a little weird.', 'start': 6067.471, 'duration': 4.785}, {'end': 6075.198, 'text': 'I feel like isLower should return true or false.', 'start': 6072.276, 'duration': 2.922}, {'end': 6078.281, 'text': "So let's scroll down to the description and return value.", 'start': 6075.238, 'duration': 3.043}, {'end': 6081.696, 'text': 'It returns, oh, this is interesting.', 'start': 6079.835, 'duration': 1.861}, {'end': 6083.457, 'text': 'And this is a convention in C.', 'start': 6081.736, 'duration': 1.721}, {'end': 6091.36, 'text': 'This function returns a non-zero int if C is a lowercase letter and 0 if C is not a lowercase letter.', 'start': 6083.457, 'duration': 7.903}, {'end': 6094.101, 'text': 'So it returns non-zero.', 'start': 6091.5, 'duration': 2.601}], 'summary': 'The islower function returns non-zero for lowercase letters, 0 for others', 'duration': 26.63, 'max_score': 6067.471, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE6067471.jpg'}, {'end': 6174.263, 'src': 'embed', 'start': 6147.305, 'weight': 2, 'content': [{'end': 6155.809, 'text': 'And so it turns out that inside of Boolean expressions, if you put a value like a function call like this that returns 0,', 'start': 6147.305, 'duration': 8.504}, {'end': 6157.07, 'text': "that's going to be equivalent to false.", 'start': 6155.809, 'duration': 1.261}, {'end': 6159.912, 'text': "It's like the answer being no, it is not lower.", 'start': 6157.39, 'duration': 2.522}, {'end': 6167.037, 'text': 'But you can also just in parentheses put the name of the function and its argument and not compare it against anything,', 'start': 6160.412, 'duration': 6.625}, {'end': 6168.739, 'text': 'because we could do something like this', 'start': 6167.037, 'duration': 1.702}, {'end': 6174.263, 'text': "Well, if it's not equal to 0, then it must be lowercase, because that's the definition.", 'start': 6168.799, 'duration': 5.464}], 'summary': 'Inside boolean expressions, a function returning 0 is equivalent to false.', 'duration': 26.958, 'max_score': 6147.305, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE6147305.jpg'}], 'start': 5666.183, 'title': 'Efficient variable declaration and utilization', 'summary': "Discusses efficient variable declaration and utilization in programming, emphasizing the use of variables to store and reuse values, the improvement in efficiency achieved by reusing variable values, and the syntactic improvement through the use of for loops to declare multiple variables at once. additionally, it covers a c program named uppercase.c for converting lowercase characters to uppercase using ascii values and the ctype.h library, demonstrating the program's functionality and comparing different approaches to achieve the same result.", 'chapters': [{'end': 5742.631, 'start': 5666.183, 'title': 'Efficient variable declaration and utilization', 'summary': 'Discusses efficient variable declaration and utilization, highlighting the use of variables to store and reuse values, the improvement in efficiency achieved by reusing the value of a variable, and the syntactic improvement achieved through the use of for loops to declare multiple variables at once.', 'duration': 76.448, 'highlights': ["The chapter emphasizes the use of variables to store and reuse values, as demonstrated by the example of storing the string length of 's' in a variable 'length' for repeated usage.", "Efficiency is improved by reusing the value of a variable, as illustrated by the optimization achieved through reusing the value of the 'length' variable in the code.", 'The syntactic improvement achieved through the use of for loops to declare multiple variables at once is showcased, highlighting the more elegant and efficient approach to variable declaration within a loop.']}, {'end': 6375.98, 'start': 5742.651, 'title': 'C program for uppercasing strings', 'summary': "Discusses the creation of a c program named uppercase.c to convert lowercase characters to uppercase using ascii values and the ctype.h library, with a demonstration of the program's functionality and a comparison of different approaches to achieve the same result.", 'duration': 633.329, 'highlights': ['The program demonstrates the manipulation of strings in C by creating a program named uppercase.c to capitalize the beginning of the user-input string by converting lowercase characters to uppercase using ASCII values and mathematical operations.', 'The chapter emphasizes the use of the ctype.h library in C to employ pre-defined functions like isLower and toUpper for efficiently checking and converting characters to uppercase, simplifying the code and improving readability.', 'The presenter discusses the use of ASCII values and mathematical operations to convert characters from lowercase to uppercase, illustrating the logic behind the conversion process and the specific ASCII values used for the transformation.', "Through the demonstration and explanation of the program's code, the chapter underscores the importance of utilizing existing library functions, such as isLower and toUpper, to streamline the coding process and improve the overall efficiency of the program."]}], 'duration': 709.797, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE5666183.jpg', 'highlights': ['The syntactic improvement achieved through the use of for loops to declare multiple variables at once is showcased, highlighting the more elegant and efficient approach to variable declaration within a loop.', "The chapter emphasizes the use of variables to store and reuse values, as demonstrated by the example of storing the string length of 's' in a variable 'length' for repeated usage.", "Efficiency is improved by reusing the value of a variable, as illustrated by the optimization achieved through reusing the value of the 'length' variable in the code.", 'The program demonstrates the manipulation of strings in C by creating a program named uppercase.c to capitalize the beginning of the user-input string by converting lowercase characters to uppercase using ASCII values and mathematical operations.', 'The chapter emphasizes the use of the ctype.h library in C to employ pre-defined functions like isLower and toUpper for efficiently checking and converting characters to uppercase, simplifying the code and improving readability.', "Through the demonstration and explanation of the program's code, the chapter underscores the importance of utilizing existing library functions, such as isLower and toUpper, to streamline the coding process and improve the overall efficiency of the program.", 'The presenter discusses the use of ASCII values and mathematical operations to convert characters from lowercase to uppercase, illustrating the logic behind the conversion process and the specific ASCII values used for the transformation.']}, {'end': 7639.989, 'segs': [{'end': 6605.796, 'src': 'heatmap', 'start': 6444.81, 'weight': 1, 'content': [{'end': 6449.932, 'text': "You might see other formats online, but they're generally not consistent with the current specification.", 'start': 6444.81, 'duration': 5.122}, {'end': 6454.475, 'text': 'This, again, was sort of the boilerplate for the simplest function we might write last week.', 'start': 6450.353, 'duration': 4.122}, {'end': 6457.577, 'text': "And recall that we've been doing this the whole time, void.", 'start': 6454.835, 'duration': 2.742}, {'end': 6465.789, 'text': "What that void means for all of the programs I have written thus far and you have written thus far is that none of our programs that we've written.", 'start': 6458.337, 'duration': 7.452}, {'end': 6467.732, 'text': 'take command line arguments.', 'start': 6465.789, 'duration': 1.943}, {'end': 6469.575, 'text': "That's what the void there means.", 'start': 6468.112, 'duration': 1.463}, {'end': 6477.003, 'text': 'It turns out that main is the way you can specify that your program does in fact take command line arguments, that is,', 'start': 6470.236, 'duration': 6.767}, {'end': 6480.604, 'text': 'words after the command in your terminal window.', 'start': 6477.003, 'duration': 3.601}, {'end': 6486.908, 'text': 'If you want to actually not use get int or get string, you want the human to be able to say something like hello David,', 'start': 6480.664, 'duration': 6.244}, {'end': 6490.909, 'text': 'and hit Enter and just print hello David on the screen.', 'start': 6486.908, 'duration': 4.001}, {'end': 6497.353, 'text': 'you can use command line arguments, words after the program name on your command line.', 'start': 6490.909, 'duration': 6.444}, {'end': 6501.214, 'text': "So we're going to change this in a moment to be something more verbose.", 'start': 6497.833, 'duration': 3.381}, {'end': 6504.937, 'text': "something that's now a bit more familiar syntactically.", 'start': 6502.435, 'duration': 2.502}, {'end': 6514.502, 'text': 'If you change that void in main to be this incantation instead int argc, comma string, argv open bracket, close bracket.', 'start': 6505.377, 'duration': 9.125}, {'end': 6519.345, 'text': 'you are now giving yourself access to writing programs that take command line arguments.', 'start': 6514.502, 'duration': 4.843}, {'end': 6526.85, 'text': 'argc, which stands for argument count, is going to be an integer that stores how many words the human typed at the prompt.', 'start': 6520.046, 'duration': 6.804}, {'end': 6529.632, 'text': 'The C automatically gives that to you.', 'start': 6527.43, 'duration': 2.202}, {'end': 6533.154, 'text': 'String argv stands for argument vector.', 'start': 6530.672, 'duration': 2.482}, {'end': 6537.897, 'text': "That's going to be an array of all of the words that the human typed at the prompt.", 'start': 6533.454, 'duration': 4.443}, {'end': 6544.562, 'text': "So with today's building block of an array, we have the ability now to let the humans type as many words or as few words as they want at the prompt.", 'start': 6537.957, 'duration': 6.605}, {'end': 6548.064, 'text': 'C is going to automatically put them in an array called argv.', 'start': 6545.102, 'duration': 2.962}, {'end': 6552.347, 'text': "And it's going to tell us how many words there are in an int called argc.", 'start': 6548.585, 'duration': 3.762}, {'end': 6556.689, 'text': "The int as the return type here we'll come back to in just a moment.", 'start': 6553.388, 'duration': 3.301}, {'end': 6561.851, 'text': "Let's actually use now this definition to make maybe just a couple of simple programs.", 'start': 6556.969, 'duration': 4.882}, {'end': 6567.033, 'text': 'But in problem set 2, will we actually use this to control the behavior of your own code?', 'start': 6561.871, 'duration': 5.162}, {'end': 6573.795, 'text': 'Let me go ahead and code up a file called argv.0, just to keep it aptly named.', 'start': 6567.393, 'duration': 6.402}, {'end': 6576.216, 'text': 'Let me go ahead and include cs50.h.', 'start': 6574.136, 'duration': 2.08}, {'end': 6579.958, 'text': 'Let me go ahead and include, oops, that is not the right name of a program.', 'start': 6576.756, 'duration': 3.202}, {'end': 6580.738, 'text': "Let's start that over.", 'start': 6580.058, 'duration': 0.68}, {'end': 6585.717, 'text': "Let's go ahead and code up argv.c.", 'start': 6582.412, 'duration': 3.305}, {'end': 6593.69, 'text': 'And here we have include CS50.h, include standard IO.h, int main not void.', 'start': 6585.737, 'duration': 7.953}, {'end': 6596.134, 'text': "Let's actually say int argc.", 'start': 6593.911, 'duration': 2.223}, {'end': 6601.112, 'text': 'string argv, open bracket, close bracket.', 'start': 6598.25, 'duration': 2.862}, {'end': 6605.796, 'text': "No numbers in between, because you don't know in advance how many words the human's going to type at their prompt.", 'start': 6601.173, 'duration': 4.623}], 'summary': 'Using int argc and string argv allows programs to take command line arguments, giving access to the number of words and the words themselves.', 'duration': 160.986, 'max_score': 6444.81, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE6444810.jpg'}, {'end': 6743.863, 'src': 'embed', 'start': 6709.064, 'weight': 2, 'content': [{'end': 6711.266, 'text': 'Dot slash argv enter.', 'start': 6709.064, 'duration': 2.202}, {'end': 6714.369, 'text': 'Huh Hello, null.', 'start': 6711.286, 'duration': 3.083}, {'end': 6716.311, 'text': 'So this is another form of null.', 'start': 6714.529, 'duration': 1.782}, {'end': 6718.914, 'text': 'But this is user error now on my part.', 'start': 6716.812, 'duration': 2.102}, {'end': 6722.096, 'text': "I didn't do exactly what I said I would.", 'start': 6720.335, 'duration': 1.761}, {'end': 6725.212, 'text': 'Yeah Yeah, I forgot the parameter.', 'start': 6722.137, 'duration': 3.075}, {'end': 6726.232, 'text': "So that's actually.", 'start': 6725.272, 'duration': 0.96}, {'end': 6731.796, 'text': "hmm, I should probably deal with that somehow, so that people aren't sort of breaking my program and printing out random things like null.", 'start': 6726.232, 'duration': 5.564}, {'end': 6735.478, 'text': 'But if I do say argv David, now you see hello David.', 'start': 6731.836, 'duration': 3.642}, {'end': 6743.863, 'text': "I can get a little curious, like what's at location 2? Well, we can see make argv bracket dot slash argv David, Enter.", 'start': 6735.838, 'duration': 8.025}], 'summary': 'A discussion about handling user errors in programming with argv and null values.', 'duration': 34.799, 'max_score': 6709.064, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE6709064.jpg'}, {'end': 6777.599, 'src': 'heatmap', 'start': 6677.838, 'weight': 0, 'content': [{'end': 6682.078, 'text': "Enter OK, it's apparently a little buggy in a couple of ways.", 'start': 6677.838, 'duration': 4.24}, {'end': 6684.661, 'text': "I forgot my backslash n, but that's not a huge deal.", 'start': 6682.118, 'duration': 2.543}, {'end': 6692.169, 'text': 'But apparently, inside of argv is literally everything the humans typed in, including the name of the program.', 'start': 6685.502, 'duration': 6.667}, {'end': 6700.178, 'text': 'So logically, how do I print out hello David or hello so-and-so and not the actual name of the program? What needs to change here? Yeah.', 'start': 6692.229, 'duration': 7.949}, {'end': 6707.743, 'text': "Yeah, so presumably index to 1 if that's the second thing I or whichever human has typed at the prompt.", 'start': 6702.418, 'duration': 5.325}, {'end': 6709.044, 'text': "So let's do make argv again.", 'start': 6707.763, 'duration': 1.281}, {'end': 6711.266, 'text': 'Dot slash argv enter.', 'start': 6709.064, 'duration': 2.202}, {'end': 6714.369, 'text': 'Huh Hello, null.', 'start': 6711.286, 'duration': 3.083}, {'end': 6716.311, 'text': 'So this is another form of null.', 'start': 6714.529, 'duration': 1.782}, {'end': 6718.914, 'text': 'But this is user error now on my part.', 'start': 6716.812, 'duration': 2.102}, {'end': 6722.096, 'text': "I didn't do exactly what I said I would.", 'start': 6720.335, 'duration': 1.761}, {'end': 6725.212, 'text': 'Yeah Yeah, I forgot the parameter.', 'start': 6722.137, 'duration': 3.075}, {'end': 6726.232, 'text': "So that's actually.", 'start': 6725.272, 'duration': 0.96}, {'end': 6731.796, 'text': "hmm, I should probably deal with that somehow, so that people aren't sort of breaking my program and printing out random things like null.", 'start': 6726.232, 'duration': 5.564}, {'end': 6735.478, 'text': 'But if I do say argv David, now you see hello David.', 'start': 6731.836, 'duration': 3.642}, {'end': 6743.863, 'text': "I can get a little curious, like what's at location 2? Well, we can see make argv bracket dot slash argv David, Enter.", 'start': 6735.838, 'duration': 8.025}, {'end': 6745.924, 'text': 'All right, so just nothing is there.', 'start': 6744.443, 'duration': 1.481}, {'end': 6751.267, 'text': "But it turns out, in a couple of weeks we'll start really poking around memory and see if we can't crash programs deliberately,", 'start': 6745.984, 'duration': 5.283}, {'end': 6757.09, 'text': "because nothing is technically stopping me from saying oh, what's at location 2 million, for instance?", 'start': 6751.267, 'duration': 5.823}, {'end': 6759.052, 'text': 'We could really start to get curious.', 'start': 6757.371, 'duration': 1.681}, {'end': 6761.033, 'text': "But for now, we'll do the right thing.", 'start': 6759.412, 'duration': 1.621}, {'end': 6765.155, 'text': "But let's now make sure the human has typed in the right number of words.", 'start': 6761.513, 'duration': 3.642}, {'end': 6765.856, 'text': "So let's say this.", 'start': 6765.195, 'duration': 0.661}, {'end': 6773.818, 'text': 'If argc equals 2, that is the name of the program and one more word after that.', 'start': 6766.676, 'duration': 7.142}, {'end': 6777.599, 'text': "go ahead and trust that in argv1, as you proposed, is the person's name.", 'start': 6773.818, 'duration': 3.781}], 'summary': 'Debugging and manipulating command line arguments in c program for printing user input.', 'duration': 99.761, 'max_score': 6677.838, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE6677838.jpg'}, {'end': 7269.459, 'src': 'embed', 'start': 7237.192, 'weight': 3, 'content': [{'end': 7244.079, 'text': 'The question is can you do things again and again at the command line like you could, with get string and get int, which by default, recall,', 'start': 7237.192, 'duration': 6.887}, {'end': 7251.606, 'text': 'are automatically designed to keep prompting the user in their own loop until they give you a stint or a float or the like? With command line arguments no.', 'start': 7244.079, 'duration': 7.527}, {'end': 7254.549, 'text': "You're going to get an error message, but then you're going to be returned to your prompt.", 'start': 7251.666, 'duration': 2.883}, {'end': 7257.632, 'text': "And it's up to you to type it correctly the next time.", 'start': 7254.589, 'duration': 3.043}, {'end': 7258.853, 'text': 'Good question.', 'start': 7258.413, 'duration': 0.44}, {'end': 7269.459, 'text': 'Yeah If you do not return a value explicitly, main will automatically return 0 for you.', 'start': 7258.894, 'duration': 10.565}], 'summary': 'Command line operations do not prompt users for input like get string and get int do. if no value is returned explicitly, main will return 0.', 'duration': 32.267, 'max_score': 7237.192, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE7237192.jpg'}], 'start': 6376, 'title': 'C programming topics', 'summary': 'Covers c programming topics such as using command line arguments, understanding exit status, text grade level analysis, and cryptography including concepts, usage, and examples.', 'chapters': [{'end': 6596.134, 'start': 6376, 'title': 'Using command line arguments in c', 'summary': "Discusses using command line arguments in c, explaining how to modify the main function to specify program's ability to take command line arguments, and the usage of argc and argv to access the number of words and the array of words typed at the prompt.", 'duration': 220.134, 'highlights': ['Main function in C can be modified to specify that the program takes command line arguments by changing void to int argc, string argv. By changing void in main to be int argc, comma string, argv open bracket, close bracket, you are now giving yourself access to writing programs that take command line arguments.', 'argc stores the number of words typed at the prompt, while argv is an array of the words typed at the prompt. argc, which stands for argument count, is going to be an integer that stores how many words the human typed at the prompt. String argv stands for argument vector, which is an array of all of the words that the human typed at the prompt.', 'The usage of argc and argv provides the ability to let users type as many words or as few words as they want at the prompt. With the usage of argc and argv, C provides the ability to let the humans type as many words or as few words as they want at the prompt, and automatically puts them in an array called argv, and tells us how many words there are in an int called argc.']}, {'end': 6973.566, 'start': 6598.25, 'title': 'Command line arguments in c', 'summary': 'Explains how to use command line arguments in c to take user input, including the use of argv, argc, and their respective roles, and the significance of context in interpreting command line inputs as strings or numbers.', 'duration': 375.316, 'highlights': ['The chapter explains how to use command line arguments in C to take user input, including the use of argv, argc, and their respective roles. It demonstrates how to take user input without using get string, by having the human type their name at the prompt, and using argv to access the user input.', 'The significance of context in interpreting command line inputs as strings or numbers. It explains how command line inputs are treated as strings due to context, and how ASCII and Unicode characters represent numbers and punctuation, necessitating the need to consider context in interpreting command line inputs.', 'The use of argv and argc in C to handle command line arguments and their roles in error handling and defensive programming. It demonstrates the use of argc to handle the number of words typed at the command line, and how to defensively program by handling cases where the user provides incorrect or unexpected input.']}, {'end': 7295.545, 'start': 6974.366, 'title': 'Understanding exit status in c programming', 'summary': 'Introduces the concept of exit status in c programming, emphasizing the importance of using return values to signal program success or failure, with the convention of returning 0 for successful execution and a non-zero value for errors, providing up to 4 billion possible exit statuses to signify errors, and setting the stage for solving actual problems in upcoming programming tasks.', 'duration': 321.179, 'highlights': ['The concept of exit status in C programming is introduced, emphasizing its importance in signaling program success or failure. The chapter explains the significance of exit status in C programming, highlighting its role in indicating whether a program succeeded or failed when automating tests, and the convention of using return values from main to signal success or failure.', 'The convention of returning 0 for successful program execution and a non-zero value for errors is illustrated, providing up to 4 billion possible exit statuses to signify errors. The importance of returning 0 for successful program execution and a non-zero value for errors is emphasized, with the insight that an int data type provides up to 4 billion possible exit statuses, allowing for a wide range of error codes to be indicated.', 'The setting of the stage for solving actual problems in upcoming programming tasks is mentioned, hinting at the relevance of exit status in the context of problem-solving in programming. The chapter contextualizes the concept of exit status in C programming, highlighting its relevance in solving actual problems in the upcoming programming tasks, particularly in problem set 2 and beyond, indicating its practical significance in programming tasks.']}, {'end': 7451.671, 'start': 7296.71, 'title': 'Text grade level analysis', 'summary': "Discusses the analysis of text grade levels using factors such as word complexity, sentence length, and sophistication, exemplified by the grade levels of the books 'one fish, two fish, red fish, blue fish' and 'harry potter', ranging from pre-grade one to grade seven.", 'duration': 154.961, 'highlights': ["The grade level of text is determined by factors such as word complexity, sentence length, and sophistication, exemplified by the grade levels of the books 'One Fish, Two Fish, Red Fish, Blue Fish' and 'Harry Potter', ranging from pre-grade one to grade seven.", 'Analyzing text involves considering the number of words, sentences, and letters in the text, and using a well-defined formula to determine the grade level of the text.', "The book 'One Fish, Two Fish, Red Fish, Blue Fish' is at a very young or early grade level due to its simple phrases, short sentences, and lack of verbs, potentially even before grade one.", "In contrast, the text from 'Harry Potter' assumes an older and more mature audience due to its longer length, use of different types of words, and inclusion of commas and phrases, indicating a higher grade level, potentially grade seven."]}, {'end': 7639.989, 'start': 7451.691, 'title': 'Cryptography and caesar cipher', 'summary': 'Discusses the concept of cryptography and the caesar cipher, which encrypts messages by shifting each letter by a certain number, ensuring secure communication, exemplified by the process and reversibility.', 'duration': 188.298, 'highlights': ['The chapter discusses the concept of cryptography and the Caesar cipher, which encrypts messages by shifting each letter by a certain number. It explains the concept of cryptography and the Caesar cipher as a method of encrypting messages by shifting each letter by a certain number, ensuring secure communication.', 'The process of encrypting and decrypting messages using the Caesar cipher is explained, exemplified by the process and reversibility. It illustrates the process of encrypting and decrypting messages using the Caesar cipher, demonstrating its reversibility and how the recipient can decrypt the message by reversing the encryption process.', 'The need for a key to encrypt and decrypt messages using the Caesar cipher is highlighted, emphasizing the importance of both parties agreeing on the key to ensure secure communication. It emphasizes the need for a key in encrypting and decrypting messages using the Caesar cipher, highlighting the importance of both parties agreeing on the key to ensure secure communication.']}], 'duration': 1263.989, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/v_luodP_mfE/pics/v_luodP_mfE6376000.jpg', 'highlights': ['C provides the ability to let users type as many words or as few words as they want at the prompt using argc and argv.', 'The chapter explains how to use command line arguments in C to take user input, including the use of argv, argc, and their respective roles.', 'The concept of exit status in C programming is introduced, emphasizing its importance in signaling program success or failure.', 'The grade level of text is determined by factors such as word complexity, sentence length, and sophistication.', 'The chapter discusses the concept of cryptography and the Caesar cipher, which encrypts messages by shifting each letter by a certain number.']}], 'highlights': ['The chapter discusses the four automatic processes involved in compiling C code: preprocessing, compiling, assembling, and linking.', 'The process of compiling C code into machine code using the make command and the Clang compiler is explained.', 'The chapter introduces the concepts of compiling and debugging, highlighting the inevitability of writing buggy code.', 'Arrays in C store multiple values contiguously in memory using a single variable.', 'The program dynamically acquires three different scores and puts them in three different locations, resulting in a better-designed program.', 'The standardization of string lengths in memory for efficiency is discussed, highlighting the benefits in terms of memory usage and performance increases.', 'Computers store spaces as the decimal number 32 or a pattern of 0s and 1s, representing all US English keys, including emojis and other languages.', 'The syntactic improvement achieved through the use of for loops to declare multiple variables at once is showcased, highlighting the more elegant and efficient approach to variable declaration within a loop.', 'C provides the ability to let users type as many words or as few words as they want at the prompt using argc and argv.']}