Removing spaces in a string, MIPS assembly - string

Question

I have a small problem with a program i'm trying to write. Basically i'm prompting a user for input. I then count the number of spaces in the string, and display the count. I also need to print out the original string with spaces removed.
The bug I'm having is when i'm adding characters to my string without spaces, it only adds the first character. $t2 is the register that is holding the character to be added, and I've checked the registers during run-time to be sure the value there was changing. I don't know where else to look.
.data
str: .space 81 # buffer for input string
strNS: .space 81 # buffer for string w/o spaces
prompt: .asciiz "Enter a string up to 80 characters\n"
head1: .asciiz "\nOriginal String: "
head2: .asciiz "\nNumber of spaces: "
head3: .asciiz "\nWith spaces removed: "
.text
main:
#print the first prompt and get the input string from console
li $v0, 4 #load syscall value to print string into $v0
la $a0, prompt #address of prompt to print
syscall #print prompt to console
li $v0, 8 #load syscall value to read input string
la $a0, str #addr of allocated space for input string is now in $a0
li $a1, 81
syscall
jal countSpace
addi $t1, $v0, 0 #the count of spaces is in $v0, save it into $t1
li $v0, 4 #print header then the count
la $a0, head1
syscall
la $a0, str #print the original string
syscall
la $a0, head2 #print second header before printing count
syscall
li $v0, 1
addi $a0, $t1, 0 #place the count in $a0
syscall #print the count
li $v0, 4
la $a0, head3 #print the third header
syscall
la $a0, strNS #print no spaces string
syscall
End:
li $v0, 10 #load syscall value for exit
syscall #exit
countSpace:
la $s0, strNS
addi $sp, $sp, -12 #adjust the stack pointer for saving
sw $s0, 8($sp) #store addr of nospace string
sw $ra, 4($sp) #store return addr on the stack
sw $a0, 0($sp) #store the count on the stack
#Begin counting spaces
addi $t3, $a0, 0 #$t3 has addr of user input
addi $t5, $s0, 0 #$t5 has addr of string with no spaces
li $t6, 0 #$t6 holds index of string with no spaces
li $t0, 0 #$t0 will hold the count of spaces
li $t4, 0 #$t4 holds the index of the string
loop:
add $t1, $t3, $t4 #$t1 = addr of str[i]
lb $t2, 0($t1) #$t2 = character in str[i]
beq $t2, $zero, exitCS #break from loop if $t2 contains null character
addi $a0, $t2, 0 #place value to be checked in $a0
#save values onto stack from temp registers to preserve them
addi $sp, $sp, -28 #adjust the stack pointer for 5 values
sw $t6, 24($sp) #save index of string with no spaces
sw $t5, 20($sp) #save addr of string with no spaces
sw $t4, 16($sp) #save index of user input
sw $t3, 12($sp) #save the addr of user input
sb $t2, 8($sp) #save the character in str[i]
sw $t1, 4($sp) #save the address of str[i]
sw $t0, 0($sp) #save the count of spaces
jal isSpace #result from this jump and link will be in $v0 after call
#pop saved values from the stack, then reset the pointer
lw $t6, 24($sp)
lw $t5, 20($sp)
lw $t4, 16($sp)
lw $t3, 12($sp)
lb $t2, 8($sp)
lw $t1, 4($sp)
lw $t0, 0($sp)
addi $sp, $sp, 28 #reset stack pointer
beq $v0, $zero, addTo #if not a space, continue to next character
addi $t0, $t0, 1 #if it is a space, increment count
addTo:
bne $v0, $zero, nextChar #If character is a space, branch
sll $t7, $t6, 2 #index if nospaces string stores width of 4
add $t7, $t7, $t5 #now $t7 points at nospaces[i]
sb $t2, 0($t7) #store the character in the nospaces string
addi $t6, $t6, 1 #increment the index of nospaces
nextChar:
addi $t4, $t4, 1 #increment the index value
j loop #jump back to loop and continue processing
exitCS:
addi $v0, $t0, 0 #count of spaces placed into $v0
addi $v1, $t5, 0
lw $ra, 4($sp) #load return addr from the stack
lw $a0, 0($sp) #load value to check from the stack
addi $sp, $sp, 8 #reset stack pointer
jr $ra #return
isSpace:
addi $sp, $sp, -12 #adjust stack pointer to make room
sw $s0, 8($sp)
sw $ra, 4($sp) #store value of return addr onto stack
sw $a0, 0($sp) #store value to check onto stack
#Check to see if the character is a space
li $t0, 32 #ascii value for space character loaded into $t0
li $v0, 0 #Set default return to 0, or "not a space character"
bne $t0, $a0, endSC #if ascii values match, character is a space
li $v0, 1 #$v0 = 1 means it is a space character
endSC:
lw $s0, 8($sp)
lw $ra, 4($sp) #restore return address
lw $a0, 0($sp) #restore addr of str
addi $sp, $sp, 12 #reset the stack pointer
end: jr $ra

Answer 1

Change sll $t7, $t6, 2 to move $t7, $t6. There's no need to align anything manually.
Here's the data segment of your program after a run with the input here's some spaces. Once you see the bug, the fix should be obvious.