Creating a variable for GUI.Button, is it possible?

Hi, my problem is every time I try to use this script I get an error. It says "Unexpected symbol 'public", I don't know if I'm just writing my variable wrong or if I'm doing everything wrong, but some help would be appreciated. I'm basically making a GUI Button, it appears fine and it lets me click to the first Level like I want it to, but I wanted to disable it after it goes to the first level. Should be pretty simple, but I'm probably thinking about it too hard. This is the script, thanks:

using UnityEngine;
using System.Collections;

public class MainMenu : MonoBehaviour {

public GUISkin gSkin;

void OnGUI () {
public bool menubutton= GUI.Button(new Rect(Screen.width/2,Screen.height/2,250,100), "Play"); //line where the error consists
if (menubutton)
Application.LoadLevel(0);
menubutton = false;

}
}

 

Remove the public before bool menubutton = ...

Please use code tags when posting code, like that you can also refer to the exact line number and post the complete error message here.
http://forum.unity3d.com/threads/using-code-tags-properly.143875/