CS50: Essential Programming Concepts

Welcome!

• All essential programming concepts from Scratch, like functions, conditionals, loops, and variables, are fundamental in any programming language.
• Source code, readable by humans, is converted into machine code (binary) by a compiler.

Visual Studio Code for CS50

• Visual Studio Code (VS Code) is used as the integrated development environment (IDE) for this course because it comes pre-loaded with all necessary software.
• VS Code can be accessed at cs50.dev.
• VS Code includes a file explorer, a text editor, and a command-line interface (CLI).
• Common command-line arguments include: cd (change directory), cp (copy files), ls (list files), mkdir (make directory), mv (move files), rm (remove files), and rmdir (remove directories).

Hello World

• Commands to write, compile, and run a program: code hello.c (creates a file), make hello (compiles the file), and ./hello (runs the program).
• code hello.c creates a file for typing instructions.
• make hello compiles the C file into an executable file.
• ./hello runs the executable program.
• printf is a function that outputs a line of text, and \n creates a new line.
• hello.c can be read by the compiler; hello is an executable file that can be run.

From Scratch to C

• The printf function in C displays text on the screen, similar to the say block in Scratch.
• \n is an escape character that creates a line break.
• Other escape characters include \r (return to the start of a line), \" (print a double quote), \' (print a single quote), and \\ (print a backslash).

Header Files and CS50 Manual Pages

• #include tells the compiler to use the capabilities of the stdio.h library (a header file), including the printf function.
• A library is pre-written code and functions that can be used in programs.
• The Manual Pages explain what various commands do and how they function.
• cs50.h is a CS50 library that includes functions like get_char, get_double, get_float, get_int, get_long, and get_string.

Hello, You

• get_string function gets a string from the user.
• %s is a format code in printf that tells the function to expect a string.
• A variable is a holding place for data; answer is a variable of type string.
• Data types include int, bool, char, and string.

Types

• Format codes for printf: %s (string), %i (int).
• Available data types in C: bool, char, float, int, long, string.

Conditionals

• Conditionals allow for different outcomes based on conditions.
• if (x < y) executes code if x is less than y; else executes code if the condition is false.
• else if allows for multiple conditions to be checked.

Operators

• Operators are mathematical operations: + (addition), - (subtraction), * (multiplication), / (division), % (remainder).

Variables

• An int variable can be assigned a value: such as int counter = 0;
• counter = counter + 1; increments the value of counter by 1.
• counter++; is another way to increment counter by 1.
• counter--; decrements the value of counter by 1.

compare.c

• Create variables using int x = get_int("What's x? ");
• make compare compiles the code, and ./compare runs it.
• Flow charts can be used to examine the efficiency of code.

agree.c

• A char is a single character, whereas a string is a series of characters.
• Single quotes are used for single characters ('y').
• == checks if two values are equal.
• || means "or" and allows for multiple conditions to be checked.

Loops and cat.c

• while loops allow you to repeat code as long as a condition is true.
• Example

 int i = 3;
    while (i > 0)
    {
        printf("meow\n");
        i--;
    }