how to make a textbox show me double? : I am trying to get myself used to c#, currently I am using SharpDevelop for that Task, anyway, I have a simple question, lets say I want to have a TextBox that Shows me the outcome of a mathematical code as shown below, how do I get the TextBox to actually Show me types like double, int or other stuff? It always tells me it cant convert double to string or whatever, I am pretty noob so yeah. 
		

    void CmdWriteClick(object sender, EventArgs e)
	   	{
			double var = 8.40;
			double start = 9.00;
			double end = var + start;
			textbox_end.Text = end;
		}

I already tried to not use the .text but something like .value but didnt work, any help? 

thanks