C# how to check for a palindrome number-CodePudding

I tried to solve this problem: check if the number is a palindrome, I know that there are a lot of examples on the Internet, but I don't understand why my code isn't working.

using System;
class HelloWorld {
    static void Main() {
        int number = 122;
        int reverse = 0;
        while(number!=0){
            reverse = (reverse*10)   number;
            number/=10;
        }
        Console.Write(reverse);
        if(number==reverse){
            Console.WriteLine("The number is palindrom");
        }
        else{
            Console.WriteLine("The number isn't palindrom");
        }
    }
}

I know that I shouldn't use int number = 122; but this was my way to understand if the code is working.

CodePudding user response：

You should save your original number. In your case number is always 0 when comparing to the reverse number.

using System;
public class HelloWorld {
    public static void Main() {
        int number = 1222111;
        int tmp_number = number;
        int reverse = 0;
        while(tmp_number!=0){
            reverse = (reverse*10)   tmp_number;
            tmp_number/=10;
        }
        Console.Write(reverse);
        if(number == reverse){
            Console.WriteLine(" The number is palindrom");
        }
        else{
            Console.WriteLine(" The number isn't palindrom");
        }
    }
}

CodePudding user response：

Within you while loop you alter the value of number until it's 0. So you always end up comparing

if (0==reverse){

CodePudding user response：

The magic happens in the loop: (reverse*10) "shifts" your result to the next place. number is basically the remainder. With number/=10 you go to the next place until there is nothing left.

It's useful to use the debugger in order to understand what happens.

CodePudding user response：

It would be easier to convert it to a string:

using System;
using System.Linq;
                    
public class Program
{
    public static void Main()
    {
        int number = 1221;
        
        // convert to string, reverse it, join it, parse it to an int
        int reversed = int.Parse( string.Join("", number.ToString().Reverse()));
        
        if(number == reversed)
            Console.WriteLine("The number is palindrom");
        else
            Console.WriteLine("The number isn't palindrom");
    }
}

You don't need to parse it back to an int, but your example uses integers.

CodePudding user response：

This is rather an approach I have followed from general pseudocodes available for multiple programming languages for implementing a palindrome program

class Solution{
public static void Main(string[] args){
   int number = 123;
   if(IsPalindrome(number))
      Console.WriteLine(number " is a palindrome number");
   else
       Console.WriteLine(number " is not a palindrome number");
  }
static bool IsPalindrome(int m){
   int total=0;
   int num=m;
   while(num != 0){
     //get the remainder
     int temp = num;
     total =total  temp*temp*temp;
      //decrement the loop variable
     num=/10;
   }
   //check and return a value to the calling method
    if(total==m)
      return true;
    else
      return false;
  }
}