Swap the value of 2 variable without using any additional variable

Write a function to swap the value of 2 variable without using any additional variable. The change should be permanent.

#include<stdio.h>

int main()
{
int a,b;
printf("\n Enter the 1st Number: ");
scanf("%d",&a);

printf("\n Enter the 1st Number: ");
scanf("%d",&b);

a=a+b;
b=a-b;
a=a-b;

printf("\n First Number = %d",a);
printf("\n Second Number = %d",b);

return 0;

}