⚙️ C Programming Masterclass Notes

Dennis Ritchie's Procedural Architecture, GCC Compilation Pipeline, Memory Layout (Stack vs Heap), Pointers & Dereferencing, Dynamic Allocation (malloc/free) aur Structures ka complete guide.

Curriculum Index

1. Module 1: Introduction to C & The 4-Stage GCC Pipeline
2. Module 2: Data Types, Format Specifiers & Operators
3. Module 3: Control Flow (Branching & Loops)
4. Module 4: Memory Layout of a C Program
5. Module 5: Pointers & Memory Address Dereferencing
6. Module 6: Dynamic Memory Allocation (malloc, calloc, free)
7. Module 7: User-Defined Types (struct, union & typedef)

Module 01

1️⃣ Introduction to C & The 4-Stage Compilation Pipeline

Definition: C ek general-purpose, procedural computer programming language hai jise 1972 me Dennis Ritchie ne Bell Labs me develop kiya tha. Isse "Mother of all modern languages" kaha jata hai kyunki modern OS (Linux, Windows kernel), databases (MySQL), aur runtimes (Python/Node) C/C++ me likhe gaye hain.

Stage	Tool	Input → Output File	Core Responsibility
1. Preprocessing	Preprocessor	prog.c → prog.i	Macros replace karna (#define), header files expand karna (#include).
2. Compilation	Compiler (GCC)	prog.i → prog.s	Clean C code ko target hardware ki Assembly Language me translate karna.
3. Assembly	Assembler	prog.s → prog.o	Assembly mnemonics ko binary machine code (Object file) me convert karna.
4. Linking	Linker	prog.o → a.out / prog.exe	C Standard Library functions (printf) ko object file se bind karna.

# Complete Compilation Command:
gcc -Wall -O2 main.c -o myprogram
./myprogram

Module 02

2️⃣ Data Types, Format Specifiers & Sizes

Data Type	Memory Size (64-bit OS)	Format Specifier	Value Range
int	4 Bytes (32 bits)	%d or %i	-2,147,483,648 to +2,147,483,647
char	1 Byte (8 bits)	%c	-128 to 127 (or 0 to 255 unsigned)
float	4 Bytes	%f	6 decimal places precision
double	8 Bytes	%lf	15 decimal places precision
pointer	8 Bytes	%p	Hexadecimal RAM address

Module 03

3️⃣ Control Flow & Functions

Execution order control karne ke liye branching aur looping constructs:

#include <stdio.h>

// Function Declaration (Prototype)
int calculateFactorial(int n);

int main() {
    int num = 5;
    printf("Factorial of %d is: %d\n", num, calculateFactorial(num));
    return 0;
}

// Function Definition
int calculateFactorial(int n) {
    if (n <= 1) return 1;
    return n * calculateFactorial(n - 1); // Recursion
}

Module 04

4️⃣ Memory Layout of a C Program

Jab koi compiled C binary RAM me load hoti hai, toh wo 5 distinct segments me divide hoti hai:

Memory Segment	Lifetime	Managed By	Stored Data
Stack	Function call end hone tak	CPU automatically	Local variables, parameters, return addresses (Fast).
Heap	Manual allocation / free	Programmer manually	Dynamic memory (malloc, calloc) (Grows upwards).
BSS Segment	Program execution tak	OS Loader	Uninitialized global aur static variables (Zero-filled).
Data Segment	Program execution tak	OS Loader	Explicitly initialized global & static variables.
Text / Code	Program execution tak	Read-Only Memory	Compiled binary CPU machine instructions.

Module 05

5️⃣ Pointers & Memory Address Dereferencing

Pointer: Ek aisa variable jo kisi doosre variable ka physical hexadecimal RAM address hold karta hai.

• & (Address-Of Operator): Variable ka RAM address return karta hai.
• * (Dereference Operator): Pointer jis address ko point kar raha hai, us address par rakhi actual value return ya update karta hai.

int x = 25;
int *ptr = &x;   // ptr holds the memory address of x (e.g. 0x7ffd9a)

printf("Value of x: %d\n", x);         // 25
printf("Address of x: %p\n", &x);      // 0x7ffd9a
printf("Value via ptr: %d\n", *ptr);   // 25 (Dereferenced)

*ptr = 100; // Mutates original x directly in RAM!
printf("New value of x: %d\n", x);     // 100

Live C Pointer & Memory Architecture Simulator

[RAM Architecture Simulator]: Ready. Click an action above to inspect Stack Memory addresses...

Module 06

6️⃣ Dynamic Memory Allocation (DMA)

Runtime par heap memory allocate aur deallocate karne ke 4 core functions (<stdlib.h>):

Function	Syntax	Behavior
malloc()	ptr = (int*) malloc(5 * sizeof(int));	Heap me raw bytes allocate karta hai (Contains garbage values).
calloc()	ptr = (int*) calloc(5, sizeof(int));	Memory allocate karke saare bytes ko 0 se initialize karta hai.
realloc()	ptr = realloc(ptr, 10 * sizeof(int));	Existing allocated memory block ka size expand ya shrink karta hai.
free()	free(ptr); ptr = NULL;	Heap memory release karta hai (Memory Leak prevent karne ke liye).

Dangling Pointer Warning: Jab aap memory ko free(ptr) kar dete hain, par pointer ko NULL assign nahi karte, toh wo ek invalid deallocated memory ko point karta rehta hai (Dangling Pointer). Isse program crash ho sakta hai.

Module 07

7️⃣ User-Defined Types: struct vs union

Criteria	struct	union
Memory Allocation	Har member ke liye dedicated alag memory (Sum of all members).	Sabhi members ek hi common memory space share karte hain (Size of largest member).
Accessing Members	Sabhi members ko ek sath simultaneously access kiya ja sakta hai.	Ek time par sirf ek hi member valid value hold kar sakta hai.

// Typedef Struct Definition
typedef struct {
    int id;
    char name[50];
    float gpa;
} Student;

int main() {
    Student s1 = {101, "Rahul Sharma", 8.95};
    printf("ID: %d | Name: %s | GPA: %.2f\n", s1.id, s1.name, s1.gpa);
    return 0;
}