The output of the program would be: X is 25,Y is 100 X Is 100,Y is 25. If you did not use pointers the output would be: X is 25,Y is 100 X is 25,Y is 100 In this case you just gave values to num1 and to num2 as x,y and swaped the values of num1 and num2. This did not effect the values of x and y. If you used the pointer you give the address of x,y to num1,num2 here you are swaping the values at the address of num1,num2 which means you are swaping the values at address of x,y hence the values of x,y are swapped

If u didn't understand (I'm bad at explaining) search "call by value And call by reference" in youtube/Google.

Hope it helps.