Needed string in program is "unused" C#

I've been making a text adventure game in C# (to learn more about strings and such). I have about 3 random scenarios that are triggered after the 10 basic ones where you start. One of them is the monkey temple. The "menu" class has two arguments, MainArgs and takenDump. In the scenarios you can choose to take a dump, and will say "there's a poop next to you" if takenDump is true (bool). MainArgs is used to go back to the same scenario if you use an unrecognized command.

public void ConScen1()  
{  
    string MainArgs;  
    bool takenDump; // Available commands are: "hit monkey talk to monkey suicide go inside"  
    string conchoice1;  
    Console.WriteLine("You arrive at a temple dedicated to the monkey god.");  
    Console.WriteLine("Outside is a monkey, presumably guarding the place.");  
    Console.WriteLine("What do you do?");  
    Console.Write(">");  
    conchoice1 = Console.ReadLine();  
    if (conchoice1.Contains("hit monkey"))  
    {  
        Console.WriteLine("You hit the monkey. He draws a knife.");  
        Console.WriteLine("He stabs you in the eye. You bleed to death.");  
        Console.WriteLine(" -- Game Over --");  
        Console.WriteLine("Press any key to start over..");  
        Console.ReadKey();  
        takenDump = false;  
        MainArgs = "null";  
        TextAdventure1.AdventureTime.Menu(MainArgs, takenDump);  
    }  
}

The problem here is the "string MainArgs;" line. I need it to call Menu() with "null" to start over. However, the studio says that it is unused (even though it's used in the if statement). Is there any way to disable the warning or fix the issue? If I remove the line, it gives me an error about how MainArgs isn't declared (in the if statement).