Address and dereference operators

Introduction

We use address and dereference operators to work with memory locations directly. This helps us access or change the value stored in a specific place in the computer's memory.

When you want to find the memory address of a variable.

When you want to access or change the value stored at a specific memory address.

When working with pointers to handle dynamic data or arrays.

When passing large data to functions efficiently by passing addresses instead of copies.

Syntax

C

int *pointer;  // declare a pointer to int
pointer = &variable;  // & is the address operator
value = *pointer;  // * is the dereference operator

The & operator gives the address of a variable.

The * operator accesses the value stored at the address the pointer holds.

Examples

Here, p stores the address of x. Using *p gets the value of x.

C

int x = 10;
int *p = &x;  // p holds the address of x
int y = *p;   // y gets the value 10 from x

Using *ptr = 20; changes the value stored at the address ptr points to, which is a.

C

int a = 5;
int *ptr = &a;
*ptr = 20;  // changes value of a to 20

Sample Program

This program shows how to get the address of a variable using &, access its value using *, and change the value through the pointer.

C

#include <stdio.h>

int main() {
    int num = 7;
    int *p = &num;  // p stores address of num

    printf("Value of num: %d\n", num);
    printf("Address of num: %p\n", (void*)&num);
    printf("Value stored at pointer p: %d\n", *p);

    *p = 15;  // change value of num using pointer
    printf("New value of num after change: %d\n", num);

    return 0;
}

Important Notes

Always initialize pointers before dereferencing to avoid errors.

Use (void*) cast when printing addresses with %p for portability.

Summary

The & operator gets the address of a variable.

The * operator accesses or changes the value at a given address.

Pointers store addresses and allow indirect access to variables.