Swaping of numbers with using 3rd num

#include<iostream.h>
#include<conio.h>
 void main()
 {
 int a,b;
 clrscr();
 cout<<"Enter 1st no.\n";
 cin>>a;
 cout<<"Enter 2nd no.\n";
 cin>>b;
 cout<<"Before swapping\n";
 cout<<"a="<<a;
 cout<<"b="<<b;
 cout<<"\nAfter swapping\n";
 a=a+b;
 b=a-b;
 a=a-b;
 cout<<"a="<<a;
 cout<<"b="<<b;
 getch();
 }