How to reverse a number as an integer and not as a string?

Question

I came across a question \"How can one reverse a number as an integer and not as a string?\" Could anyone please help me to find out the answer? Reversal should reverse the

Answer 1

This should do it:

int n = 12345;
int left = n;
int rev = 0;
while(Convert.ToBoolean(left)) // instead of left>0 , to reverse signed numbers as well
{
   int r = left % 10;   
   rev = rev * 10 + r;
   left = left / 10;  //left = Math.floor(left / 10); 
}

Console.WriteLine(rev);

Answer 2

Yay! A bling way. (No, really. I hope that this is more a "How would I do..." question and not something you really need in production)

public int Reverse(int number) {
  return int.Parse(number.ToString().Reverse().Aggregate("", (s,c) => s+c));
}

Answer 3

As per Pritam Karmakar comment , Yes this will not work when given number has 0 at end. If you pass number as 150 it will return 51 not 051. so i had write code to display number in Reverse order as per user input please check this.

int reverseNum = 0, reminder, num;
        Console.WriteLine("Enter Number to Reverse:");
        int.TryParse(Console.ReadLine(), out num);
        bool isZero = false;
        int cnt=0;
        while (num > 0)
        {
            reminder = num % 10;
            reverseNum = (reverseNum * 10) + reminder;
            num = num / 10;
            if (reverseNum == 0)
                isZero = true;                
            cnt++;
        }
        if (isZero)
        {
            Console.WriteLine(reverseNum.ToString().PadLeft(cnt, '0'));
        }
        else
        {
            Console.WriteLine(reverseNum);
        }
        Console.ReadKey();

Answer 4

Solution suggested by @jerjer and @cfern is perfect but It will not work for negative int number like -1234507.

Solution : If number is negative int then multiply by -1 after that call your method ReverseInt(-1234507)

    int number = -1234507;
    **number = number > 0 ? number : (number * -1);**

    int reverseNumber = 0;

    while(number > 0){
        reverseNumber = (reverseNumber * 10) +  (number % 10) ;
        number = number / 10;
    }
    Console.WriteLine(reverseNumber);

Answer 5

a new one:

using System;
using System.Linq;

public class Program
{
    public static void Main()
    {
        int i = 234;
        int j = -123;
        Console.WriteLine(reverse(i));
        Console.WriteLine(reverse(j));
    }

    static int reverse(int i)
    {
        int sign = i / Math.Abs(i);
        var abs = string.Concat(Math.Abs(i).ToString().Reverse());
        return int.Parse(abs) * sign;
    }
}

https://dotnetfiddle.net/VGJJFf

Answer 6

    /// <summary>
    /// Reverse a int using its sting representation.
    /// </summary>
    private int ReverseNumber(int value)
    {
        string textValue = value.ToString().TrimStart('-');

        char[] valueChars = textValue.ToCharArray();
        Array.Reverse(valueChars);
        string reversedValue = new string(valueChars);
        int reversedInt = int.Parse(reversedValue);

        if (value < 0)
           reversedInt *= -1;

        return reversedInt;
    }