CS0447 Project 3
                       Due March 29th midnight

PROJECT: Write a program in MIPS ssembly language that behaves as follows:

Repeatedly ask the user for input.  The input can be a positive or
negative decimal integer, or +,*,or p.  While the user types in
numbers, they should be put into a queue.  When the user enters +,
your program should list all the numbers in the queue and their sum
(as shown below), and then set the queue to have just the sum in it.
Similarly, if the user enters *, it should list all the numbers and
their product, and set the queue to have just the product.  When the
user enters p, your program should output the first number in the
queue in decimal, binary, and hexadecimal formats, and then exit.
Your program should behave correctly when the user types +,*, or p
when there are zero, one, ore more integers in the queue.  Note that
the sum of no numbers is zero, and the product of no numbers is 1.
You don't have to worry about overflow.  That is, if the answer is too
big to fit into 32 bits, it's ok if your program doesn't work
correctly.  You can also assume that all numbers will be at most 10
digits.  You can implement the queue with an array that you declare
yourself.  Thinking about the basic ideas used with the program stack
(pushing, popping, etc.) may help you to think about how to implement
the queue.  You may assume that at most 16 numbers will ever be in the
queue at a time, but if the user tries to enter more, you should give
an error message, and keep the previous contents of the queue.

WHAT TO SUBMIT:

You will submit one file with the extension .s (an assembly language
program).  Copy a file called yourfirstname_yourlastname.s
to /afs/cs.pitt.edu/usr0/moir/public/447/submission_3 

SAMPLE RUN:

Input: 12
Input: 15
Input: -10
Input: +
12+15-10=17
Input: 3
Input: *
17*3=51
Input: 8
Input: +
51+8=59
Input: p

Base   Output
-------------
10       59
2        0000 0000 0000 0000 0000 0000 0011 1011
16       0x0000003b

HELP:

To help you get started, here is a piece of code that reads in an
expression from the user and stores it to an array.  The example
checks through the expression and prints out 'yes' if it contains a
'+' and 'no' otherwise.  Your program doesn't have to do anything like
that - this is just an example you can use to figure out how to access
individual characters in the string, etc.

# This piece of code accepts a string of input, prints it out, and says "yes" 
# if the string contains a "+" and "no" otherwise

.data
v:    	.asciiz " ()0123456789*+-"	# string of ascii chracters we will use
exp: 	.space 128 		       	# memory to store input string
no:	.asciiz "no"
yes:	.asciiz "yes"

.text
.globl main
main:	li $v0, 8
	li $a1, 127 			#maximum size for input expression
	la $a0, exp
	syscall				#read input expression into exp	

	la $a0, exp			#print the string in exp
	li $v0, 4
	syscall
	
# This part is an example on how to access a character in a string
# It merely checks for a "+" in an expression if there is one prints "yes"
# otherwise prints a "no".

	la $t0, exp             	#prepare to access characters in exp
	la $t1, v               	#prepare to access a character in v
	lb $t3, 14($t1)			#load "+" ascii into a register
        li $t4, 0xa                     #load end-of-line into $t4
loop2:	lb $t2, 0($t0)			#load next array element
	beq $t2, $t3, hi		#if it's a "+", go to print yes
	addi $t0, $t0, 1		#increment loop counter
	bne $t2, $t4, loop2		#check for null (end of string), 
					#continue if not found
	li $v0, 4			#print no
	la $a0, no
	syscall
	j exit

hi:     li $v0, 4			#print yes
	la $a0, yes
	syscall

exit:	li $2, 10			#exit program
	syscall