C# Using Variables for GUI Rectangles

In Unityscript I never had a problem doing something like this:

 var screeenPosition : Vector2;
 
 function OnGUI () {
 
 GUI.Label (Rect(screenPosition.x, screenPosition.y, 200, 100), "Hello World");
 
 }

or this:

 var labelRectangle : Rect = (0,0, 100, 200);
 
 function OnGUI () {
 
 GUI.Label (labelRectangle, "Hello World");
 
 }

However, in C# I cannot use variables in the rectangles of the GUI.x functions like this, it runs but it doesn't display anything, at all. Only constants in the rectangle parameters work. Help?