Palindrome - error

Question

I'm quite new to C# and I was making a small application to check if the input of the console is a palindrome. I came pretty far by myself, but I got stuck with an error.

Code:

class Program
{
    static void Main(string[] args)
    {
        string str;
        Console.WriteLine("Voer uw woord in:");
        str = Console.ReadLine();

        if (isPalindroom(str) == true)
        {
            Console.WriteLine(str + " is een palindroom");
        }
        else
        {
            Console.WriteLine(str + " is geen palindroom");
        }

    }

    bool isPalindroom(String str)
    {
        string reversedString = "";
        for (int i = str.Length - 1; i >= 0; i--)
        {
            reversedString += str[i];
        }
        if (reversedString == str)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

I get this error:

Error 1 An object reference is required for the non-static field, method, or property 'ConsoleApplication2.Program.isPalindroom(string)' snap 17 17 ConsoleApplication2

Which is at:

if (isPalindroom(str) == true)

If you could help me a bit, I'd be very pleased :)

Answer 1

Simply add static modifier to your isPalindroom method.

If you don't, isPalindroom will be an "instance" method, that can be called on a Program instance.

To be simple, as you don't have a variable of kind Program (main method itself is static), you can't call a non-static method.

A static method can be called either on the type itself (Program.isPalydroom(xxx) or from any other method in the class.

Answer 2

Make the function static:

static bool isPalindrome(String str)
{
}

The Main() method is static (by requirement) and thus it can only call static members.

And because your bool isPalindrome() is a 'pure' function, ie it only requires data from its parameters, it can be static.

Small nitpick: always use PascalCasing for method names, IsPalindrome