.data
str: 	.space 41 	# create char buffer, 40 chars + null
nl: .asciiz "\n" 	# newline
.text
.globl main
main:
	# get input
	li $v0,8 	# service code to read string
	la $a0,str 	# address of buffer
	li $a1,41 	# buffer length
	syscall
	li $t0,0	 # push null value onto stack. used to identify end of string
	addi $gp,$gp,-4	 # alternatively can use sub 4
	sw $t0,($gp) 	# bottom of stack
	li $t1,0 	# the index of the first char

# push each character onto the stack
push:

	lb 	$t0,str($t1)	 # get char
	beqz 	$t0,strend 	# if null, go to strend

	addi 	$gp,$gp,-4 	# move down the stack
	sw	 $t0,($gp) 	# store the char

	addi 	$t1,1 	# add 1 to the index
	j 	push 	# jump back to push for loop
strend:

# pop chars from stack back into the buffer
	li 	$t1,0 	# index of first byte of str
pop:
	lw 	$t0,($gp) 	# pop char from stack
	addi 	$gp,$gp,4
	beqz 	$t0,done 	# if null, go to done (end of string)

	sb 	$t0,str($t1)	 # store byte in $t1
	addi 	$t1,1 		# add 1 to the index
	j 	pop 		# jump back to pop for loop
done:

# print the reversed string
	li	 $v0,4 		# service code
	la	 $a1,str 	# address of string
	syscall

#returns to new line after reverse printed
	li $v0, 4
	la $a0, nl
	syscall

#exits the program
	li 	$v0,10
	syscall