How do I convert type string to System.Windows.Form.TextBox?

Try the following. I think this is close to what you need.

TextBox[] tba = new TextBox[4];

for (int p = 1; p <= 4; p++)

{

	TextBox tb = new TextBox();

	tb.Text = "whatever";

	tb.Top = p * 20;

	tba[p - 1] = tb;

	panel1.Controls.Add(tb);

}

Note that the code is putting the textboxes in an array, and you can later use the array to get the values from the textboxes.

show this link you may get some idea

http://www.experts-exchange.com/Programming/Languages/.NET/.NET_Framework_2.0/Q_23847736.html

http://www.infernodevelopment.com/creating-c-average-calculator

http://msdn.microsoft.com/en-us/library/system.windows.forms.binding.aspx