LAB 3

Due February 2, 9PM


Multi-base adding machine

This is an ungraded programming assignment -- see syllabus for
information on how it will be counted.

This project builds on the numeric I/O of the previous assignment to
make a multi-base adding machine.

Rather than ask for a base and a number in a loop, you will read in
commands and numbers where, adding-machine like, the commands are
unprompted (though is an invalid command or number is put in, you
should give the user some help).

The adding machine will have 6 functions:

+   Add a number to the current sum
-   Subtract a number from the current sum 
=   Print current sum
z   Zero the current sum
#   Prompt user for a base change  (always base 10, without commas)
x   Exit
    

All numbers entered are unsigned (since we can add and subtract)
Results are signed:  print a + or - with each answer, since we can't
use the traditional red and black of adding machines.

The system will work with bases from 2..60 (with an initial base of 10)

For input and output, use the comma notation of lab 2.

For example:

<<Informatively prompt user to enter numbers or commands>>
+1,0
#75
<<Base must be in range 2-60. Reenter base:>> 2
<<Number base is now 2>>
+1,0
=
<<+1,1,0,0>>
#16
<<Number base is now 16>>
=
<<+12>>
z
#60
<<Number base is now 60>>
+10,12
=
<<+10,12>>
#10
<<Number base is now 10>>
=
<<+6,1,2>>
+C
<<Digit C is out of range in base 10>>
+1,2
=
<<6,2,4>>
-6,3,0
=
<<-6>>
x
<<Thank you for using the 12C calculator!>>

Notes:

1.  Use the input routines from the previous assignment.
    You should be able to use your multi-digit reading routine for
    entering bases (numbers in base 10 between 2 and 60).

2.  Error messages are important:  what errors can come up?
    A few are illustrated above.

6.  The main program will call the routines depending on the control
    characters. (+, -, =, #, z, x).  It will read a single character
    which will indicate the command to be performed (or an informative
    error message if it is not one of the 6 characters above), and
    then move into a 'case' statement structure (ie,
    if-elseif-elseif-...) to process each command.  The + and -
    commands will read a number in the current base and process it.
    The = command will print out the sum in the current base.
    The # command will read a number in base 10, print out a message
    about the new base (in base 10), and set the current base.
    The z command has no input or output, but resets the accumulator.
    The x will print a closing prompt and end the program.

    Apart from the case of x, you will keep looping to read in a new
    command. 

Optional:
   a.  Include additional operators
   b.  For bases <= 16, do I/O without the commas
   c.  Check for overflow
   d.  Nice error messages.

Handin:
    calc.spim:  The well documented code
    README:  Name and email address, and answers to:
      a.  If you did not implement to two different I/O formats,     
          write a few sentences about how you would.
      b.  What ASM statements would you use to check for overflow in
          arithmetic operations?
      c.  What ASM statements would you use to check for overflow in
          data input (ie, numbers that are too large).

Grading:
    10:  README with questions answered, program
     8:  README without questions answered but with code comments
     7:  No readme
     5:  No calc.spim but great readme
     0:  No readme and no calc.spim

Checkoff:
     -1     Late Checkoff (Wednesday; no latter)
     -1	    Not quite fully functional
     -2     Not entirely functional
     -3     Almost entirely not functional
     -4     No checkoff