Perform swapping without using a third variable

//pgm to perform swapping without using a third variable
#include<iostream.h>
#include<conio.h>
void main()
{
    int a,b;
    clrscr();
    a=10;
    b=20;
    a=a+b;
    b=a-b;
    a=a-b;
    cout<<"a="<<a<<endl;
    cout<<"b="<<b;
    getch();
}