Ndtyjky

I'm asking a user for input and I want to replace each character of the word by the number of uppercase characters in this word

Example:
Input: AaAA
output: 3333 (4 letters - 3 uppercase)

The part for counting upercase letters in a word works (stored in $t5)

However I cannot replace e.g "3333" with "AaAA". I'm trying to do it using sb in word_replace section. In my output I can see boxes instead of numbers.

Here is my code:

.data

prompt: .asciiz "Enter a string: "

msgout: .asciiz "Output string: "

input:  .space  256

output: .space  256

    .text

    .globl main



main:

    li  $v0, 4          # Print enter a string prompt

    la  $a0, prompt     

    syscall



    li  $v0, 8          # Ask the user for the string they want to reverse

    la  $a0, input      # We'll store it in 'input'

    li  $a1, 256        # Only 256 chars/bytes allowed

    syscall



    la  $t2, ($a0)      # t2 - input string



    word:

        li  $t1, 0              # Normal counter

        li  $t5, 0              # Uppercase counter



        word_countUppercase:

            add $t3, $t2, $t1       # $t2 is the base address for our 'input' array, add loop index

            lb  $t4, 0($t3)     # load a byte at a time according to counter    



            bltu    $t4, ' ', word_prereplace   # We found end of word



            addi    $t1, $t1, 1     # Advance our counter (i++)



            bltu    $t4, 'A', word_countUppercase

            bgtu    $t4, 'Z', word_countUppercase



            addi    $t5, $t5, 1         # Advance our counter (i++)

            j   word_countUppercase



        word_prereplace:

            la  $t2, ($a0)      # t2 - input string

            li  $t1, 0          # Normal counter



            word_replace:

                add $t3, $t2, $t1       # $t2 is the base address for our 'input' array, add loop index

                lb  $t4, 0($t3)     # load a byte at a time according to counter    



                bltu    $t4, ' ', exit      # We found end of word



                sb  $t5, output($t1)    # Overwrite this byte address in memory 



                addi    $t1, $t1, 1         # Advance our counter (i++)

                j   word_replace





exit:

    li  $v0, 4          # Print msgout

    la  $a0, msgout

    syscall



    li  $v0, 4          # Print the output string!

    la  $a0, output

    syscall



    li  $v0, 10         # exit()

    syscall