Visual C++ - Edit Box & variable precision

In Visual C++ 4.0, I have created 4 edit boxes and placed
 them on a dialog box. I have assigned a floating point
variable to each edit box. Next to each box I have a radio
button. By checking the radio button for one of the edit
 boxes, the relevant edit box will become disabled.
By changing the values of the other three edit boxes the
disabled box's value will change. The problem is how do
I change the amount of decimal places displayed in the
disabled edit box. I would also like to change the color
of the result if it goes out of range.