Program to swap two numbers without using 3rd number

//Program to swap two numbers without using 3rd number
#include<stdio.h>
#include<conio.h>
void main()
{
   int a, b;
   clrscr();
   printf("Enter two integers values\n");
   scanf("%d%d", &a, &b);
   // let a = 11, b = 13
   printf("The numbers before swapping are\n");
   // Printing of a = 11 and b = 13
   printf("1st Number = %d\n2nd Number = %d\n\n",a,b);
   a = a + b; // a = 11 + 13 = 24
   b = a - b; // b = 24 - 13 = 11
   a = a - b; // a = 24 - 11 = 13
   printf("The numbers after swapping are\n");
   //Printing of a = 13 and b = 11
   printf("1st Number = %d\n2nd Number = %d",a,b);
   getch();
}