C# Exercise: 131 Function Palindrome, recursive

// Import the System namespace to use basic classes like Console
using System;

class Program
{
    // Recursive function to check if a string is a palindrome (symmetric)
    public static bool Palindrome(string str)
    {
        // Convert the string to uppercase to make the comparison case-insensitive
        str = str.ToUpper();

        // Base case: if the string has one or zero characters, it's a palindrome
        if (str.Length <= 1)
        {
            return true;
        }

        // Compare the first and last characters
        if (str[0] != str[str.Length - 1])
        {
            return false; // If they are not equal, it's not a palindrome
        }

        // Recur with the substring excluding the first and last characters
        return Palindrome(str.Substring(1, str.Length - 2));
    }

    // Main function to test the Palindrome function
    public static void Main()
    {
        // Test case 1: "RADAR"
        string testString1 = "RADAR";
        Console.WriteLine($"Is \"{testString1}\" a palindrome? {Palindrome(testString1)}");

        // Test case 2: "HELLO"
        string testString2 = "HELLO";
        Console.WriteLine($"Is \"{testString2}\" a palindrome? {Palindrome(testString2)}");

        // Test case 3: "madam"
        string testString3 = "madam";
        Console.WriteLine($"Is \"{testString3}\" a palindrome? {Palindrome(testString3)}");
    }
}