Enable and Disable Buttons

The first change in the code is an instance variable for the ok button. We treat the button as a window when we write code for the BN_DISABLE message.
The button disable command is found under the ok button.

The code checks to see if each of the fields contains a non-trival string.

void ProfDlg::OkBNDisable ()
{
     // INSERT>> Your code here.
     int ok = _firstName->GetWindowTextLength() > 0 &&
         _lastName->GetWindowTextLength() > 0 &&
         _initial->GetWindowTextLength() > 0 &&
         _phone->GetWindowTextLength() > 0 &&
         _office->GetWindowTextLength() > 0;

     okButton->EnableWindow(ok);
}

Finally to make sure this function is called whenever one of the fields is updated, for each field we add a handler for the EN_CHANGE message. This message is found under each instance variable. Each of these handlers consists of a call to OkBNDisable.