GUI Button to toggle true false when pressed

Questions & Answers
1

if(GUI.Button(Rect(150,700,50,50),"Cast")) { ShowPowers = true; }

this is to bring up a button menu however i want it so that if the button is pressed again the ShowPowers = false; please help thanx :)

2 
if(GUI.Button(Rect(150,700,50,50),"Cast")) { ShowPowers = !ShowPowers; }