# pread -- prompt for and read an integer
#
# on entry:
#    $ra -- return address
#
# on exit:
#    $v0 -- the integer

pread:   
         la    $a0,prompt        # print string
         li    $v0,4             # service 4
         syscall
        
         li    $v0,5             # read int into $v0
         syscall                 # service 5
        
         jr    $ra               # return
         nop                     # branch delay slot
        
         .data
prompt:
         .asciiz "Enter an integer: "

Main Program

Assume that the subroutine is correct. Now write the main program.

         .text
         .globl  main

main:
         jal     _____            # read first integer
         nop                      #  
         move    $s0,$v0          # save it in $s0

         jal     _____            # read second integer
         nop                      # 
         move    $s1,$v0          # save it in $s1

         jal     _____            # read third integer
         nop                      #  
         move    $s2,$v0          # save it in $s2
         
         addu    $s0,$s0,$s1      # compute the sum
         addu    $a0,$s0,$s2
         
         li      $v0,1            # print the sum
         syscall
         
         li      $v0,10           # exit
         syscall