modify text property of control where ctrl name is variable (C#)

hey,
normal update of text property is easy.  control on the form has an id of txtPercent1, so something like
txtPercent1.text = "new value";
works perfectly.

however, i need to update the text property of a texbox control, where the ID of the texbox control is generated and stored in variable name.  i need to loop thru a set of textboxes on the form and update the value of each box.  i've tried using FindControl(), but i still cannot access the text property.  There has to be a way to do this....
code to illustrate:
        Control ctrl;
     
        // loop thru all boxes [txtPercent1, txtPercent2, txtPercent3]
        for (int i = 1; i <= 3; i++)
        {
         &nb ...