A Fine Example

Sometimes you will have to remove the null at the end of the input string, perhaps because it is intended to be part of a larger string. Other times, as in the following example, you can use two print string operations.

The example program asks the user to enter a person's name followed by comma and "enter". Then the program writes out a personalized letter using the name. The body of the letter is printed using only one syscall. The personalized greeting is printed first in a separate syscall because it is null terminated.

# overdue.asm

        .text
        .globl  main

main:   
        # get patron name
        li      $v0,4           # print prompt
        la      $a0,prompt      #
        syscall
        li      $v0,8           # code 8 == read string
        la      $a0,name        # $a0 == address of buffer
        li      $a1,24          # $a1 == buffer length
        syscall                 # Invoke the operating system.

        # print the letter
        li      $v0,4           # print greeting
        la      $a0,letter      #
        syscall
        li      $v0,4           # print body
        la      $a0,body        #
        syscall

        li      $v0,10      # exit
        syscall

        .data
prompt: .asciiz "enter name, followed by comma-enter: "
letter: .ascii  "\n\nDear "
name:   .space  24

body:   .ascii  "\nYour library books are way\n"
        .ascii  "overdue.  Please return them\n"
        .ascii  "before we give your name\n"
        .asciiz "to the enforcement squad.\n\n"

It is somewhat crude to make the user enter a comma at the end of the name. It would be nicer to have the program detect the end of the name and automatically put a comma after it. The program would be much longer.