comparing dynamic int value to reverse of its value, not comparing properly.

Question

import java.util.Scanner;

@SuppressWarnings("all")
public class Palindrome {

public static void main(String[] args) {
// TODO Auto-generated method stub

System.out.println("Enter any number to check if its palindrome or not :");

Scanner sc = new Scanner(System.in);

int num = sc.nextInt();

int rev = 0,temp;

//temp = num;

while(num != 0) {

rev = rev * 10;

rev = rev + num%10;

num = num / 10;

}

System.out.println(rev);

if(rev == num) {
System.out.println("Its a palindrome number");
}else {
System.out.println("Its not a palindrome number");
}

}

}

when comparing 2 int values whether they are same or not, in this palindrome program, the control is going to the "ELSE" part, but if I assign the "num" value to "temp" and in IF clause if i give -> if(rev == temp), then its working properly. Why is it happening like this??

Answer 1

Because by the time the while...loop completed, <num> will be zero.

If you save a copy of <num> value into <temp>, and you compare <rev> against <temp> (instead of <num>) after the while...loop, then it really doesn't matter even though <num> became zero after the while...loop

The point is, we gotta have a copy of the original number to be compared against the reversed version of it.

Answer 2

Gotcha, thank you✨