MIPS- Reading integers error - arrays

Question

# Programming Project 2
# Noah Heath
# #02685972
.data # Data declaration
# A+B -(C-D x E)
string1: .asciiz "Please enter an integer from range 0 to 32768: "
string2: .asciiz "Next integer: "
string3: .asciiz "Invalid input. Start over. "
userinput: .space 100
var6: .asciiz "The result of A+B -(C-D x E) is: "
.text
main:
la $a0, string1 #load string one and print
li $v0, 4
syscall
la $a1, userinput
li $t1, 5 #set temporary variable to 5
li $t0, 0 #start of counter
input:
beq $t0, $t1, exit
li $v0, 5 # read integer
syscall
blt $v0, $zero, input # if input is less than zero
bgt $v0, 32768, input # if input is greater than 32768
sw $v0, 0($a1)
addiu $a1, $a1, 4
exit:
la $t3, userinput # stores base address of user input array into $t3
lw $t4, ($t3) # load first number
lw $t5, 4($t3) # load second number
lw $t6, 8($t3) # load third number
lw $t7, 12($t3) # load fourth number
lw $t8, 16($t3) # load fifth number
add $s1, $t4, $t5 # adds 1 and 2 into $t0
mult $t7, $t8 # multiplies 2 and 3
mflo $s2 # retrieves from register
sub $s3, $t6, $s2 # subtracts 7 from 6
sub $s4, $s1, $s3 # subtracts 1 from 3
move $a0, $s4 # moves result into a0
li $v0, 1 # instruction to print result
syscall # call operating system to perform operation
li $v0, 10 # exit instruction
syscall
I'm been trying to figure out the reason that my code isn't reading the user integers and storing. I'm sure everything is syntactically correct. Can someone help me understand if I'm using the registers wrong?
QTSpim says Exception occurred at PC = 0x00400060.
Then goes on to say unaligned address in store= 0x1001005b.
It goes on in increments of 4(I'm assuming because of the way the array is indexed.
Final Error message is
Exception 5 [Address error in store] occurred and ignored
Exception 4 [Address error in inst/data fetch] occurred and ignored(repeats 4 times)

Answer 1

There's nothing wrong with the code that asks for user input.
I guess your problem is that you are trying to store what the user entered in a non-aligned address (the line that issues sw $v0, 0($a1) ).
You should add a directive .align 2 before your userinput label, e.g.:
string3: .asciiz "Invalid input. Start over. "
.align 2
userinput: .space 100