Question

This code gets an integer n and displays all palindrome numbers less than n.
But seems the for loop doesn’t work; because when I enter a number except 0, 1 and negatives, nothing happens.
I tried debugging, but couldn’t find the problem!

Sample input: 30

Sample output: 1 2 3 4 5 6 7 8 9 11 22

import java.util.Scanner;

public class PalindromeNumbers {
    public static void main(String args[]) {
        Scanner input = new Scanner(System.in);
        int n = input.nextInt();
        if (n == 0 || n == 1 || n < 0)
            System.out.println("There's no Palindrome Number!");
        else {
            for (int num = 1; num < n; num++) {
                int reversedNum = 0;
                int temp = 0;
                while (num > 0) {

                    // use modulus operator to strip off the last digit
                    temp = num % 10;

                    // create the reversed number
                    reversedNum = reversedNum * 10 + temp;
                    num = num / 10;

                }
                if (reversedNum == num)
                    System.out.println(num);
            }
        }
    }
}

Answer 1

You run into an infinite loop: you use num in your for loop as an index, and reset it to 0 inside the loop. Use different variables, and it should work!

for (int i = 1; i < n; i++) {
    int num = i;

    ...

    if (reversedNum == i)
        System.out.println(i);
}