Wap in ‘C’ to find swap two numbers without using third variable.

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