Furthermore, it sounds like they've already have shown you how to make a menu.
When I execute your program, I must get a menu (similar to the one
that was implemented in my very first email) that allows me to first
choose which of the above four functions I would like to implement,
second it must allow me to input the first argument of the function
I just chose, and finally it must allow me to input the second argu-
ment of the function (for the first two functions, I should be able
to enter a character, while for the last two functions, I must be
able to enter a string of characters).