Write a C# program to check if a number is Palindrome or not

A palindrome is a number or string that reads the same forward and backward. In C#, we can check if a number is a palindrome by reversing its digits and comparing it with the original number.

Syntax

Following is the syntax for reversing a string using Array.Reverse() method −

char[] charArray = string.ToCharArray();
Array.Reverse(charArray);
string reversedString = new string(charArray);

Following is the syntax for comparing strings ignoring case −

bool isEqual = string1.Equals(string2, StringComparison.OrdinalIgnoreCase);

Using String Reversal Method

The most straightforward approach is to convert the number to a string, reverse it, and compare with the original −

using System;

class Program {
    static void Main(string[] args) {
        string string1, rev;
        string1 = "Madam";
        char[] ch = string1.ToCharArray();

        Array.Reverse(ch);
        rev = new string(ch);

        bool b = string1.Equals(rev, StringComparison.OrdinalIgnoreCase);
        if (b == true) {
            Console.WriteLine("String " + string1 + " is a Palindrome!");
        } else {
            Console.WriteLine("String " + string1 + " is not a Palindrome!");
        }
    }
}

The output of the above code is −

String Madam is a Palindrome!

Using Numeric Approach for Numbers

For numeric palindromes, we can reverse the digits mathematically without converting to string −

using System;

class Program {
    static void Main(string[] args) {
        int number = 12321;
        int originalNumber = number;
        int reversedNumber = 0;

        while (number > 0) {
            int digit = number % 10;
            reversedNumber = reversedNumber * 10 + digit;
            number = number / 10;
        }

        if (originalNumber == reversedNumber) {
            Console.WriteLine(originalNumber + " is a Palindrome!");
        } else {
            Console.WriteLine(originalNumber + " is not a Palindrome!");
        }
    }
}

The output of the above code is −

12321 is a Palindrome!

Using Two-Pointer Approach

For strings, we can use two pointers moving from both ends toward the center to check characters −

using System;

class Program {
    static void Main(string[] args) {
        string text = "racecar";
        bool isPalindrome = true;
        int left = 0;
        int right = text.Length - 1;

        while (left < right) {
            if (char.ToLower(text[left]) != char.ToLower(text[right])) {
                isPalindrome = false;
                break;
            }
            left++;
            right--;
        }

        if (isPalindrome) {
            Console.WriteLine(text + " is a Palindrome!");
        } else {
            Console.WriteLine(text + " is not a Palindrome!");
        }
    }
}

The output of the above code is −

racecar is a Palindrome!

Comparison of Approaches

Conclusion

Checking for palindromes in C# can be done using string reversal, numeric digit manipulation, or two-pointer comparison. The choice depends on whether you're working with strings or numbers, and whether memory efficiency is important for your application.