为什么这提示不起作用？ MIPS

Question

# PART 1 

    .data   # Data declaration section
sourceprompt:   .ascii  "Enter a source string: "

queryprompt:    .ascii  "Enter a query string: "

replaceprompt:  .ascii  "Enter a replace string: "

nomatch:    .ascii  "Nothing to replace "

source:         .space  256 

query:          .space  256

replace:        .space  256

    .text

main:                       # Start of code section

    li $v0, 4               # Load system call for printing into $v0
    la $a0, sourceprompt            # Load address of string into $a0
    syscall                 # call operating system to perform operation

    li $v0, 8               # Load system call for reading string into $v0
    la $a0, source              # Load byte space into source so string has a place to go
    li $a1  256             # Set the byte space for the string
    syscall

    move $t1, $a0               #move source out of a0 so it doesn't get replaced  

    li $v0, 4               # Load system call for printing into $v0
    la $a0, queryprompt         # Load address of string into $a0
    syscall                 # call operating system to perform operation

    li $v0, 8               # Load system call for reading string into $v0
    la $a0, query               # Load byte space into buffer so string has a place to go
    li $a1  256                 # Set the byte space for the string
    syscall                 # call operating system to perform operation

    move $t2, $a0               #move query into t2


    li $v0, 4               # Load system call for printing into $v0
    la $a0, replaceprompt           # Load address of string into $a0
    syscall                 # call operating system to perform operation

    li $v0, 8               # Load system call for reading string into $v0
    la $a0, replace             # Load byte space into buffer so string has a place to go
    li $a1  256                 # Set the byte space for the string
    syscall                 # call operating system to perform operation

    move $t3, $a0               #move replace into t3

PRINTS

  

输入源字符串：输入查询字符串：输入替换字符串：   无需替换

我不想那样！我希望它一个一个地提示！为什么要做htat？!!

Answer 1

这些字符串不会以空值终止。请改用.asciiz。