Can a user defined function be called from an event handler? [on hold]

I am a beginner.I am trying to make a calculator using visual c++ 2012 and i want to know whether a user defined function can be called from an event handler.

Suppose if button 2 or 2 or 3 or ..... is pressed call a function that prints 1 or 2 or 3...... in a textbox ! If its possible supply a code using:

A button event handler where it calls a function say void f and prints text of the button in textbox .

In CLR project