Program to swap two numbers without using 3rd variable

void main()
{
int a,b;
clrscr();
printf("\n enter First Number :");
scanf("%d",&a);
printf("\n enter Second Number :");
scanf("%d",&b);
swap(&a,&b);
printf("\n first Number is : %d",a);
printf("\n second Number is : %d",b);
getch();
}

swap(int *a,int *b)
{
*a=*a-*b;
*b=*a+*b;
*a=*b-*a;

}