Java Program to Reverse a Number in Java Using Loop

• Java program to reverse a number using while loop and using a function.

Given a number N, we have to reverse the sequence of digits of a N and print it on screen. After reversing the least significant digit will become the most significant digit and vice versa. In general the i^th digit from left becomes the i^th digit from right side of N.

For Example,
Input Number : 6534211
Output Number : 1124356

Algorithm to reverse digits of a number

• Get the least significant digit(right most digit) of N. rightDigit = N%10;
• Append it at the end of reverse number. reverse = (reverse * 10) + rightDigit;
• Remove right most digit from number. N = N/10;
• Repeat this process till N is greater than zero.

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Java program to reverse a number using while loop

In this program we first take a number as input from user and store it in variable N and then reverse N by implementing above mentioned algorithm using a while loop. Here, we are using while loop but same can be implemented using a for or do-while loop also. Finally we print the reversed number on screen.

package com.tcc.java.programs;

import java.util.Scanner;

/**
 * Java Program to reverse a number
 */
public class ReverseNumber {
    public static void main(String[] args) {
        int N, reverse = 0, rightDigit;
        Scanner scanner;
        scanner = new Scanner(System.in);

        System.out.println("Enter an Integer");
        N = scanner.nextInt();

        while (N != 0) {
            rightDigit = N % 10;
            reverse = (reverse * 10) + rightDigit;
            N = N / 10;
        }
        System.out.format("Reversed Number = %d\n", reverse);
    }
}

Output

Enter an Integer
98765
Reversed Number = 56789

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Java program to reverse the digits of a number using function

This java program is similar to above program except here we are using a user defined function "getReverseNumber" which takes an integer N as input parameter and returns it's reversed number.

package com.tcc.java.programs;

import java.util.Scanner;

/**
 * Java Program to reverse a number using function
 */
public class ReverseNumberFunction {
    public static void main(String[] args) {
        int N;
        Scanner scanner;
        scanner = new Scanner(System.in);

        System.out.println("Enter an Integer");
        N = scanner.nextInt();

        // Calling getReverseNumber method to reverse digits of N
        System.out.format("Reversed Number = %d\n", getReverseNumber(N));
    }

    /**
     * Reverses the digits of a number
     */
    public static int getReverseNumber(int N) {
        int reverse = 0, rightDigit;
        while (N != 0) {
            rightDigit = N % 10;
            reverse = (reverse * 10) + rightDigit;
            N = N / 10;
        }
        return reverse;
    }
}

Output

Enter an Integer
12034
Reversed Number = 43021

Enter an Integer
4
Reversed Number = 4