Explain reference and pointer in C programming?

In C programming, pointers are variables that store memory addresses of other variables. C does not have references like C++ − it only has pointers for indirect access to variables.

Syntax

datatype *pointer_name;
pointer_name = &variable_name;

Pointers in C

• Pointers store the memory address of another variable

• They can hold NULL values

• They enable pass by reference functionality

• They can be declared without initialization

• Use * operator to access the value at the address (dereference)

• Use & operator to get the address of a variable

Example: Basic Pointer Operations

This example demonstrates pointer declaration, initialization, and dereferencing −

#include <stdio.h>

int main() {
    int a = 2, b = 4;
    int *p;
    
    printf("Address of a = %p<br>", (void*)&a);
    printf("Address of b = %p<br>", (void*)&b);
    
    p = &a; /* p points to variable a */
    printf("Value of a = %d<br>", a);
    printf("Value at *p = %d<br>", *p);
    printf("Address in p = %p<br>", (void*)p);
    
    p = &b; /* p now points to variable b */
    printf("Value of b = %d<br>", b);
    printf("Value at *p = %d<br>", *p);
    printf("Address in p = %p<br>", (void*)p);
    
    return 0;
}

Address of a = 0x7fff5fbff73c
Address of b = 0x7fff5fbff738
Value of a = 2
Value at *p = 2
Address in p = 0x7fff5fbff73c
Value of b = 4
Value at *p = 4
Address in p = 0x7fff5fbff738

Pass by Reference Using Pointers

C achieves pass by reference functionality using pointers −

#include <stdio.h>

void swap(int *x, int *y) {
    int temp = *x;
    *x = *y;
    *y = temp;
}

int main() {
    int a = 10, b = 20;
    
    printf("Before swap: a = %d, b = %d<br>", a, b);
    swap(&a, &b);
    printf("After swap: a = %d, b = %d<br>", a, b);
    
    return 0;
}

Before swap: a = 10, b = 20
After swap: a = 20, b = 10

Key Points

• C has no references − only pointers for indirect access
• Pointer declaration: int *ptr;
• Address operator: &variable gets the address
• Dereference operator: *pointer gets the value

Conclusion

Pointers are fundamental in C for dynamic memory allocation, function parameters, and efficient data manipulation. Unlike C++, C uses only pointers for indirect variable access.