MIPS addressing issue

Question

I am trying to create a string in MIPs, then change each character from the string into an integer. Currently I am having trouble creating the new string and I can't figure out what I am doing wrong. The block of code I am inserting should be creating a memory allocation for 4 characters, then assigning a number to each location and saving the string into the memory position. It doesn't seem to be saving the string however, as when I print it later it is always blank. I am only including the block of code that doesn't seem to be working.

Any tips would be greatly appreciated!

.data
string: .space 16   #declare storage for string 4 char
string2: .asciiz "Success!"
string3: .asciiz "Failure!"

.text
main:    # convert string to integer

la $t0, string      # load base address of string to reg $t0
li $t1, 1       # $t1 = 1   
sw $t1, ($t0)       # first array element set to 1
li $t1, 2       # $t1 = 2
sw $t1, 4($t0)      # second array element set to 2
li $t1, 3       # $t1 = 3
sw $t1, 8($t0)      # third array element set to 3
li $t1, 0       # $t1 = 0
sw $t1, 12($t0)     # third array element set to 0
            # array stored at #t0
sw $t0, string

li $v0, 4       # syscall for print string
la $a0, string      # load string to be printed
syscall         # print digit string

This all compiles with no issues.

Answer 1

In MIPS every character takes 1 byte (not 4), at least when using syscall 4 to print the string.

Also note that you are trying to print unprintable characters (ASCII codes 1, 2, and 3), instead of ASCII codes for '1', '2' and '3'. And I think sw $t0, string instruction shouldn't be there.

Finally, note that syscall 4 assumes the string is NULL terminated, therefore if you declare storage for 4 chars, and want to use that syscall you really have 3 characters available.

Here's a snippet of the code you posted fixed to print string 123:

.data
string: .space 4   #declare storage for string 4 char

.text
main:    # convert string to integer

la $t0, string      # load base address of string to reg $t0
li $t1, '1'       # $t1 = 1   
sb $t1, ($t0)       # first array element set to 1
li $t1, '2'       # $t1 = 2
sb $t1, 1($t0)      # second array element set to 2
li $t1, '3'       # $t1 = 3
sb $t1, 2($t0)      # third array element set to 3
li $t1, 0       # $t1 = 0
sb $t1, 3($t0)     # third array element set to 0
            # array stored at #t0

li $v0, 4       # syscall for print string
la $a0, string      # load string to be printed
syscall         # print digit string