Master C Pointers: Definition, Usage, and Practical Examples

What is a pointer in C?

A pointer is a variable that stores the memory address of another variable, allowing direct access and manipulation of the data stored at that address.

How to use pointers

Define a pointer : Use the * operator in the declaration, e.g., int *p; creates a pointer to an int.

Obtain an address : Use the address‑of operator & to get a variable’s address, e.g., p = &a; assigns the address of a to p.

Access or modify the pointed value : Dereference the pointer with * to read or write the value at that address, e.g., *p = 10; stores 10 at the location pointed to by p.

Typical use cases

Dynamic memory allocation : Functions such as malloc and free allocate and release memory at runtime.

Array and string manipulation : Pointers can traverse and modify arrays or strings efficiently.

Function parameter passing : Large structures (arrays, structs) are often passed by pointer to avoid copying overhead.

Complete example

The program below demonstrates defining a pointer, obtaining a variable’s address, accessing the value through the pointer, and modifying the original variable via the pointer.

#include <stdio.h>
int main() {
    int a = 100;
    int *p;               // define a pointer to int
    p = &a;                // obtain the address of a
    printf("Value of a: %d
", a);
    printf("Address of a: %p
", (void*)&a);
    printf("Pointer p value (address of a): %p
", (void*)p);
    printf("Value accessed via pointer p: %d
", *p);
    *p = 200;             // modify a through the pointer
    printf("Modified value of a: %d
", a);
    return 0;
}

This example prints the original value and address of a, shows the pointer’s stored address, accesses the value via *p, changes the value to 200 through the pointer, and prints the updated value.