Java Program to Reverse a Number without using Recursion

This is the Java Program to Reverse a Given Number Without Using Recursion.

Problem Description

Write a Java Program to Reverse a Given Number Without Using Recursion.

Problem Solution

Using a loop, extract the last digit of the number and add it at the end of the reverse formed till now.

Program/Source Code

Here is the source code of the Java Program to Reverse a Given Number Without Using Recursion. The program is successfully compiled and tested using IDE IntelliJ Idea in Windows 7. The program output is also shown below.

  2. //Java Program to Reverse a Given Number Without Using Recursion
  4. import;
  5. import;
  7. public class ReverseNumber {
  8.     // Function to reverse the number without using recursion
  9.     public static void main(String[] args) {
  10.         BufferedReader br = new BufferedReader(new InputStreamReader(;
  11.         int n;
  12.         try {
  13.             System.out.println("Enter a number");
  14.             n = Integer.parseInt(br.readLine());
  15.         } catch (Exception e) {
  16.             System.out.println("An error occurred");
  17.             return;
  18.         }
  19.         int rev,i,s;
  20.         rev = 0;
  21.         for(i=n; i!=0; i/=10){
  22.             rev= rev*10+(i%10);
  23.         }
  24.         System.out.println("The reverse is " + rev);
  25.     }
  26. }
Program Explanation

1. In function main(), firstly the number is taken as input.
2. Then, the loop for(i=n; i!=0; i/=10), runs until the each digit is extracted, in the reverse order.
3. The statement rev= rev*10+(i%10); adds the digit obtained to the reverse.


Time Complexity: O(1).

Runtime Test Cases
Case 1 (Simple Test Case):
Enter a number
The reverse is 422412

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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