Swapping two numbers (using two variables)

Program:

#include<stdio.h>
#include<conio.h>
void main()
{
    int a, b;
    clrscr();
    printf("Enter two numbers : ");
    scanf("%d %d", &a, &b);
    printf("\nBefore swapping : \n\n");
    printf("a = %d \t b = %d", a, b);
    a = a + b;
    b = a - b;
    a = a - b;
    printf("\n\nAfter swapping : \n\n");
    printf("a = %d \t b = %d", a, b);
    getch();
}

Output:

Enter two numbers : 10 20
Before swapping :
a = 10 b = 20
After swapping :
a = 20 b = 10