Write a program which allows the user to perform simple tasks on a

calculator. A series of methods allows the user to select an

operation to perform and then enter operands.

The first method displays a menu, giving the user the choice

of typing in any one of the following:

$+,-,*,/,$ or $\%$ representing the usual arithmetic operators

A representing the average of two numbers

X representing the maximum of two numbers

M representing the minimum of two numbers

S representing the square of a number

Q indicating the user wants to quit the program