Understanding code

[Delshire]

Hello everyone! I am doing some exercises and when i can't solve them i come to google and try to solve and understand them but i have a problem here understanding how to reverse an int. Here's the code

  bool esPal(int z)
{
	int t = z;
	int rev = 0;

	
	while (z > 0) {
		int dig = z % 10; 
		rev = rev * 10 + dig; //Don't understand how these operations reverse the number
		z = z / 10;

	

	}

Could someone explain me line by line the while loop that reverses the int? I do not get how doing the module of z and then multiplying by ten and adding can invert/reverse the string.

Thank you very much!
Delsh

[MiiNiPaa]

int dig = z % 10;

z % 10 calculates number modulo 10. If we write our number in decimal, it have same effect as read last digit.

rev = rev * 10 + dig;

Here we:
1) Multiply number by 10 (eqivalent to writng 0 at the end)
2) add digit we get from previous line. As last digit is 0 (by 1), both steps are equivalet to "write digit at the end"

z = z / 10;

Integer division eqivalent to "remove last digit"

So whole algorithm is:
1) Take the last digit of original number
2) Append it to the end of reversed number
3) Erase last digit of original
repeat.

[deathslice]

When you're doing stuff like this it's best you write it on a piece of paper so you can then understand how they got there. For example, let say Z is 15. 15 % 10 is 5.0. 0 * 10 + 5.0 = 5.0. 15 / 10 is 1.5. The loop continues. 1.5 /10 is 1.0. 5 * 10 + 1.5 is 51.5 or 51 because the integers gets truncated. So, the opposite of 15 is 51. If you want to, use any other number, work out the steps on a piece of paper, and you should then see the process unfold before your very eyes.

[Delshire]

Thank you very much guys! Much clearer now!