Translating Letters To Numerical Values

I want my code to look at a textbox to determine which letter is in it, & assign a numerical value to a second textbox, based on what letter is in the first textbox.[code]The problem is that, when I step through the code, I can see that Form20.txtGrade1.text DOES EQUAL "C", but my code skips over the part that says Form20.txtGrade1a.text = "4". Instead, if I hover over that part, I can read Form20.txtGrade1a.text = " ".When I do not step through the code, and just run it, I see the two textboxes, with the first one containing the C, and the second one is just blank.