Swapping of two numbers without using 3rd variable

#include<stdio.h>
#include<conio.h>
int main()
{
int a,b;
clrscr();
printf("enter two no.s");
scanf("%d%d",&a,&b);
printf("\n values before swapping a=%d \t b=%d",a,b);
a=a+b;
b=a-b;
a=a-b;
printf("\n values after swapping a=%d \t b=%d",a,b);
getch();
return 0;
}