Programming

• Functions
  • arguments, return values
• Conditionals
• Boolean expressions
• Loops
• Variables

C

#include <stdio.h>

int main(void)
{
    printf("Hello, world!\n");
}

Rust

fn main() {
    println!("Hello, world!");
}

Java

public class HelloWorld 
{
    public static void main(String[] args) 
    {
        System.out.println("Hello, world!");
    }
}

Python

print("Hello, world!")

JavaScript

console.log("Hello, world!");

Source Code

01111111 01000101 01001100 01000110 00000010 00000001 00000001 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000010 00000000 00111110 00000000 00000001 00000000 00000000 00000000
10110000 00000101 01000000 00000000 00000000 00000000 00000000 00000000
01000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
11010000 00010011 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 01000000 00000000 00111000 00000000
00001001 00000000 01000000 00000000 00100100 00000000 00100001 00000000
00000110 00000000 00000000 00000000 00000101 00000000 00000000 00000000
01000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
01000000 00000000 01000000 00000000 00000000 00000000 00000000 00000000
01000000 00000000 01000000 00000000 00000000 00000000 00000000 00000000
11111000 00000001 00000000 00000000 00000000 00000000 00000000 00000000
11111000 00000001 00000000 00000000 00000000 00000000 00000000 00000000
00001000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000011 00000000 00000000 00000000 00000100 00000000 00000000 00000000
00111000 00000010 00000000 00000000 00000000 00000000 00000000 00000000
...

>objdump -d hello.o  

hello.o:     file format pe-x86-64

...

0000000000000054 <main>:
  54:   55                      push   %rbp
  55:   48 89 e5                mov    %rsp,%rbp
  58:   48 83 ec 20             sub    $0x20,%rsp
  5c:   e8 00 00 00 00          call   61 <main+0xd>
  61:   48 8d 05 00 00 00 00    lea    0x0(%rip),%rax        # 68 <main+0x14>
  68:   48 89 c1                mov    %rax,%rcx
  6b:   e8 90 ff ff ff          call   0 <printf>
  70:   b8 00 00 00 00          mov    $0x0,%eax
  75:   48 83 c4 20             add    $0x20,%rsp
  79:   5d                      pop    %rbp
  7a:   c3                      ret

Machine Code

What actually happened?

• C is a compiled language.
• C's compilation process:
  1. Preprocess: gcc -E hello.c -o hello.i (expands macros, includes headers, deletes comments, creates preprocessed source code)
  2. Compile: gcc -S hello.i -o hello.s (creates assembly code)
  3. Assemble: gcc -c hello.s -o hello.o (creates object file which is machine code)
  4. Link: gcc hello.o -o hello (combines object files and libraries, creates executable file)
• Note:
  • Different compilers may have slightly different commands or steps.
  • Compilation process occurs before program execution.

What actually happened?

• Python is an interpreted language (with a compilation step.)
• Python's execution process:
  1. Parse and compile: Source code to bytecode
     • python -m py_compile hello.py (creates .pyc file)
     • python -m dis hello.py (displays readable bytecode)
  2. Interpret: Bytecode executed by Python Virtual Machine (in CPython)
• Note:
  • CPython is the default and most used interpreter, but others exist.
  • Interpreter converts source code or bytecode into machine code at runtime.
  • This process occurs line-by-line or block-by-block during execution.

print("Hello, world!")

answer = input("What is your name?")

print("Hello, " + answer)

Conditionals

if x < y:
    print("x is less than y")

if x < y:
    print("x is less than y")
else:
    print("x is not less than y")

if x < y:
    print("x is less than y")
elif x > y:
    print("x is greater than y")
else:
    print("x is equal to y")

Variables

counter = 0

counter = counter + 1

# or

counter += 1

Loop

counter = 3

while counter > 0:
    print("meow")
    counter = counter - 1

i = 3

while i > 0:
    print("meow")
    i -= 1

i = 1

while i <= 3:
    print("meow")
    i += 1

i = 0

while i < 3:
    print("meow")
    i += 1

// using C:

for (int i = 0; i < 3; i += 1)
{
    printf("meow\n");
}

// using Python:

for i in range(3):
    print("meow")

while True:
    print("meow")