Week 1 C === ###### tags: `2021-CS50` ## CS50 IDE [ide.cs50.io](https://ide.cs50.io) <font color="blue">IDE:</font> Intergrated DEvelopment Environment <font color="blue">CLI:</font> Command Line Interface <font color="blue">GUI:</font> Graphical User Interface computer can only understand 0s and 1s. So the program we write(source code), the computer can't understand，need compiler to machine code(0s and 1s). <font color="blue">Compiler:</font> convert source code to machine code. ```flow st=>start: input(source code) e=>end: output(machine code) op=>operation: Compiler st->op->e ``` ## CS50 IDE- CLI examples test ``` make hello ``` run ``` ./hello ``` <font color="blue">arguments:</font> inputs to functions. in scratch: ![](https://i.imgur.com/FJKABxR.jpg =270x200) in C: ``` X: print O: printf ``` <font color="blue">printf:</font> print a formatted something or other. ```c= printf("hello,world!"); ``` + notice: double quotes: ```" "``` semicolon: ```;``` ```flow st=>start: input(arguments) e=>end: output(side effects) op=>operation: functions st->op->e ``` <font color="blue">functions:</font> a programmed version of an algorithm, the implementation of an algorithm in code、software. a side effect of a function is often something visual that happens on the screen, like text or audio. ``` return values, variables ``` it's not going to say it on the screen. It's gonna just pass it back to the programmer, so we can reuse whatever the output of the function was. <font color="blue">library:</font> a code that someone else has written. ## string In C, we have the complete flexibility over what we want to do. In CS50, type to run the code, no quick button to play. C is an old language, decades now old. So back then, everything was deliberate. User interface was not top priority,performance instead was, for instance. But nowadays, ther are fancier intergrated development enviroments. ex: play button. <font color="blue"> String:</font> a term of art in the programming world. A "string" is text/word/letter/paragraph/a page of text. ```c= get_string("What is your name?"); ``` "=" means,effectively, copy whatever is on the right, into whatever is on the left. ```c= answer = get_string("What is your name?"); ``` but we have to tell the computer in advance what type f variable we want. ```c= string answer = get_string("What is your name?"); ``` ![](https://i.imgur.com/gkPNXih.jpg)