C Program to Swap Two Numbers Using Pointer and User Defined Function

Question: write a program in C to swap two numbers using pointer and user defined function.

C Source Code: Swap Numbers - Call by Reference

#include<stdio.h>

/* Function prototype */
void swap(int *p, int *q);

/* Main function */
int main()
{
    int first_number, second_number;

    /* Reading two numbers */
    printf("Enter first number: ");
    scanf("%d", &first_number);
    printf("Enter second number: ");
    scanf("%d", &second_number);

    printf("Before swapping: first_number = %d and second_number = %d\n", first_number, second_number);

    /* Function call, call-by-reference */
    swap(&first_number, &second_number);

    printf("After swapping: first_number = %d and second_number = %d\n", first_number, second_number);

    return 0;
}

/* Function definition */
void swap(int *p, int *q)
{
    int temp;

    /* Swapping */
    temp = *p;
    *p = *q;
    *q = temp;
}

Output

The output of the above program is:

Enter first number: 10
Enter second number: 20
Before swapping: first_number = 10 and second_number = 20
After swapping: first_number = 20 and second_number = 10