What Happens Step by Step …

You run your program (e.g., ./program)

OS loads the program from disk into RAM

CPU reads instructions from RAM and executes them

CPU may:

    Do math (+, -, &, ^)

    Compare numbers

    Jump to a different part of the program

    Read/write data in RAM

You use a compiler like gcc or clang: gcc main.c -o main This converts your human-readable code into machine code — a binary file (like main or main.exe).

The compiler:

Parses your code

Allocates memory for variables like int x

Generates instructions that your CPU can run

When you do:

./main

The Operating System (OS):#

Loads the compiled program into memory (RAM)

Sets up:

    Stack: for function calls and local variables (int x = 5)

    Heap: for dynamic memory (malloc, calloc, etc.)

    Text segment: stores machine code (your compiled functions)

    Data segment: for global/static variables

Then it starts executing your code line by line using the CPU.

Memory Layout of a C Program in RAM#

• Stack ← grows down (local variables)

• Heap ← grows up (malloc memory)

• BSS Segment (.bss) ← (uninitialized globals)

• Data Segment (.data) ← (initialized globals)

• Text Segment (.text) ← (compiled code / instructions)

Stack

📌 Stores: Function call info, local variables, return addresses

Heap

📌 Stores: Dynamically allocated memory (malloc, calloc, new in C++)

BSS Segment (.bss)

📌 Stores: Global and static variables that are uninitialized or initialized to zero

Data Segment (.data)

📌 Stores: Global and static variables that are initialized

Text Segment (.text)

📌 Instructions like printf("x = %d", x); are here

Now example in C code#

#include <stdio.h>

int g = 1;         // → .data
static int s;      // → .bss (uninitialized static)
int main() {
    int x = 5;     // → stack
    int *p = malloc(sizeof(int));  // → heap
    *p = 10;
    printf("x = %d\n", x);  // → .text for instructions
    return 0;
}