LBS290F                                                      Fall 1991

                     ASSIGNMENT 16 - A CALCULATOR

Due Date: Before Midnight 11/15/91

In this program you will write a program which simulates a simple
hand calculator which can add, subtract, multiply, and divide.

The calculator will work with floating point numbers.

The calculator program has a single display where the answer is 
always displayed after each number is entered.  This display is
called the "accumulator" (in computerese).

The calculator will repeatedly prompt for calculator commands until
the S (Stop command).  The calculator will accept the following commands:

     Command         Action

     = 1.23          Sets the accumulator to 1.23
     + 5.0           Adds 5.0 to the accumulator
     / 2.0           Divides accumulator by 2.0
     * 6.3           Multiplies the accumulator by 6.3
     - 4.0           Subtracts 4.0 from the accumulator
     S 0.0           Stops the program

There must be a space between the operator and the number.

As each command is precessed the program will print out what it is
doing and print the new accumulator value after each command has been
processed.

The program will also check for incorrect commands and print an error
message out without changing the accumulator.

An example run is as follows:

     $ a.out

            Acc=0.0
     Enter: = 1.5
     Setting accumulator to 1.5
     
            Acc=1.5
     Enter: + 9.5
     Adding 9.5 to the accumulator
     
            Acc=10.0
     Enter: Z 9.75
     ERROR: Z is not a valid command to the calculator program
     
            Acc=10.0
     Enter: / 5.0
     Dividing the accumulator by 5.0 
     
            Acc=2.0
     Enter: * 1.35
     Multiplying the accumulator by 1.35
     
            Acc=2.7
     Enter: S 0.0
     
     Calculator program finished

Hand in only the source code using mailx.