CS0447 Project 2
               Due Wednesday March 1st midnight

The purpose of this assignment is to write your first assembly
language procedures (including recursive procedures) and to write your
first loops.

WHAT TO SUBMIT:

You will submit one file with the extension .s (an assembly language
program).  You should submit it to the
/afs/cs.pitt.edu/usr0/moir/public/447/submission_2 directory.


PROJECT:

Implement a small "Calculator" in MIPS assembly language.  The
calculator should repeatedly display a menu, allow the user to choose
a function and inputs, and display the results of the calculation.
The functions you should implement are multiply, factorial, and
exponent.

These functions are defined as follows:

Multiply:  M(n,0) = 0
           For m>0, M(n,m) = M(n,m-1)+n

Factorial: F(0)=1
           For n>0, F(n)=M(n,F(n-1))

Exponent:  E(n,m)= n^m (n "to the power" m)

You should implement each of the above functions as a procedure.  Use
iteration (a loop) to implement exponent, and recursion to implement
multiply and factorial.  To help you get started with recursive
procedures, there's an example factorial procedure on p. 137 of the
book.  However, in this project, you are not allowed to use any of the
"multiply" instructions.  Thus, your factorial and exponent procedures
will have to call your multiply procedure.  Important note: these are
very inefficient ways to calculate these values - this is an exercise!

Your program should look like the following example (make sure you
assign the options in the same order as shown here).

  Press 1 for multiply
  Press 2 for factorial
  Press 3 for exponent
  Press 4 to quit

Your choice? ===> 1
Enter n ========> 2
Enter m ========> 5
The answer is 10

The program should repeatedly process options until the quit option is
selected.  If the user types an option outside the range of options,
they should get an error message and the menu should be displayed
again.  You can assume that all inputs will be positive integers.