MIPS code using stack produces a recursion error - recursion

Question

In this assignment I have to convert any given number from base 33 (1-9, A-W, and a-w) to base 10. If the input is empty, the message "Input is empty" is displayed. If input is anything else than numbers or letters A-W, output will be: "Input is invalid". This program must use stack and recursion.
I wrote my program without stack and it was working. I am now trying to transfer that into a program that uses stack but am getting the message "Input is empty", regardless of what I input.
Here is my MIPS code:
############### Base 33 to Base 10 Converter ###################
.data
userInput: .space 700
empty: .asciiz "Input is empty."
long: .asciiz "Input is too long."
invalid: .asciiz "Invalid base-33 number."
.text
ErrorLong:
#prints message for input that is too long
la $a0, long
li $v0, 4
syscall
j end
ErrorInvalid:
#prints message for invalid input
la $a0, invalid
li $v0, 4
syscall
j end
ErrorEmpty:
#prints message for empty string
la $a0, empty
li $v0, 4
syscall
j end
.globl main
main:
addi $sp, $sp, -16
li $v0, 8
la $a0, userInput
li $a1, 200
syscall
sw $a0, 0($sp) # put into stack the memory address where user input is
or $a0, $0, $0
sw $ra, 12($sp)
jal Number
lw $ra, 0($sp)
#TEST FOR END
#la $a0, strEnd
ori $a0, $a0, 4
syscall
#end
jr $ra
Number:
addi $sp,$sp,-4
lb $t8, 0($sp)
###################
Rid:
#takes care of leading spaces
li $t9, 32 # space
beq $t9, $t8, Character
move $t8, $a0 ############
j length
addi $sp,$sp,4
Character:
addi $a0, $a0, 1
j Rid
#takes care of length
length:
addi $t0, $t0, 0
addi $t1, $t1, 10
add $t2, $t2, $a0
addi $sp,$sp,-4
lb $s2, 0($sp)
#itertates through the array
traverse:
beqz $s2, discovered
beq $s2, $t1, discovered
addi $a0, $a0, 1
addi $t0, $t0, 1
j traverse
addi $sp,$sp,4
#busted empty space or input that violates limit
discovered:
#if it's empty go to case for empty which outputs
beqz $t0, ErrorEmpty
slti $t4, $t0, 5
#if it's too long, go to case for too long and print
beqz $t4, ErrorLong
move $sp, $t2
#go to next verification process
j verify
addi $sp,$sp,-4
lb $s3, 0($sp) #loads address here
#checks inputs
verify:
beqz $s3, initial
beq $s3, $t1, initial
slti $t3, $s3, 48 #invalid for anything below 0
bne $t3, $zero, ErrorInvalid
slti $t3, $s3, 58 #legal input for everything less than or equal to 9
bne $t3, $zero, Move
slti $t3, $s3, 65 #legal input for everything less than or equal to 65, 'a'
bne $t3, $zero, Move
slti $t3, $s3, 88 #legal input for anything less than or equal to 88
bne $t3, $zero, Move
slti $t3, $s3, 97 # invalid input, not numerical nor alphabetical
bne $t3, $zero, ErrorInvalid
slti $t3, $s3, 120 #legal input for lower case characters
bne $t3, $zero, Move
bgt $s3, 119, ErrorInvalid # illegal input, out of range
addi $sp,$sp,4
#now I iterate again, this time to check for invalid input
Move:
addi $sp, $sp, 1 #iterates
j verify #goes to verification point
#first step of conversion, does the prerequisite work for translation
initial:
move $a0, $t2 #moves content
addi $t5, $t5, 0 #$t5 has 0 now
add $s0, $s0, $t0
addi $s0, $s0, -1 #decrement
#load immediate puts values in registers to be used
li $s4, 3 #each digit
li $s5, 2
li $s6, 1
li $s1, 0
translate:
addi $sp,$sp,-4
lb $s7, 0($sp) #loads digits
beqz $s7, final #final conversion step
beq $s7, $t1, final #if branch statement is true, move to final conversion statement
slti $t3, $s7, 58 #checks for less than or equal to 58
bne $t3, $zero, Base #OK to move forward if $t3 is not null
slti $t3, $s7, 88 #max for upper
bne $t3, $zero, Mari #OK to go to conversion of upper characters if $t3 is not null
slti $t3, $s7, 120 #max for lower
bne $t3, $zero, Mici #OK to go to conversion of lower characters if $t3 is not null
addi $sp,$sp,4
Base:
addi $s7, $s7, -48 #conversion for regular numbers
j row
Mari:
addi $s7, $s7, -55 #conversion for upper case
j row
Mici:
addi $s7, $s7, -87 #conversion for lower case
row: #determines which digit needs to be converted
beq $s0, $s4, one
beq $s0, $s5, two
beq $s0, $s6, three
beq $s0, $s1, last
#first character
one:
li $t6, 35937 #values to multiply by for the power of 3
mult $s7, $t6
mflo $t7
add $t5, $t5, $t7
addi $s0, $s0, -1
addi $sp, $sp, 1 ####################
j translate
#second character
two:
li $t6, 1089 #values to multiply by for the power of 2
mult $s7, $t6
mflo $t7
add $t5, $t5, $t7
addi $s0, $s0, -1
addi $sp, $sp, 1 ###################
j translate
#third character
three:
li $t6, 33 #values to multiply by for the power of 1
mult $s7, $t6
mflo $t7
add $t5, $t5, $t7
addi $s0, $s0, -1
addi $sp, $sp, 1
j translate
#fourth character
last:
li $t6, 1 #values to multiply by for the power of 0
mult $s7, $t6
mflo $t7
add $t5, $t5, $t7
#no more need to go back to translation step
final: #final step
li $v0, 1
move $sp, $t5 #moves content to $a0 so it can be printed
syscall
#last system call of the program will end program
end: #prints result
li $v0, 10
syscall
jr $ra

Answer 1

In main, you save a0 (the user entered number) to 0(SP), and ra to 12(SP), then call Number.
In number, you add -4 to SP.
Ten attempt to get a byte from 0(SP)
I am assuming you are trying to get the first character from the user string ?
Since you added -4 to the stack, the a0 value you saved in 0(SP) is not at 4(sp).
The value you saved is the pointer to the string, so doing a load byte from the pointer:
So change:
lb $t8, 0($sp)
to
lw $a0, 4($sp)
lb $t8, 0($a0)
Which also means you don't need the move $t8, $a0 a couple of lines later