C program to swap two numbers without using third variable

#include<stdio.h>
#include<conio.h>

void main()
{
int a=100, b=30;
clrscr();

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

printf("Swapping without using third variable (using + and -).\n\n");
printf("Value of a=%d and b=%d.", a,b);
getch();
}