5.6: Multiple Input Parameters with PrintInt Subprogram

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When printing an integer value, the program always printed a string first to tell the user what was being printed, and then the integer was printed. This behavior will be abstracted in the following subprogram, PrintInt. In this subprogram there are two input parameters: the address of the string to print, which is stored in $a0; and the integer value to print, which is stored in $a1.

Other than passing in two parameters and creating a slightly larger subprogram, this program does not add any new material that needs a commentary section. The changes from the program in Chapter 5.5 are highlighted in yellow.

Program 5-4: Multiple input parameters with PrintInt subprogram

# File:        Program5-2.asm
# Author:      Charles Kann
# Purpose:     To illustrate implementing and calling a subprogram named PrintNewLine.
.text
main:
    # read an input value from the user
    la $a0, prompt
    jal PrintString
    li $v0, 5
    syscall
    move $s0, $v0
    
    # print the value back to the user
    jal PrintNewLine
    la $a0, result
    move $a1, $s0
    jal PrintInt
    
    # call the Exit subprogram to exit
    jal Exit
.data
    prompt: .asciiz "Please enter an integer: "
    result: .asciiz "You entered: "
# subprogram:    PrintNewLine
# author:        Charles Kann
# purpose:       to output a new line to the user console
# input:         None
# output:        None
# side effects:  A new line character is printed to the user's console
.text
PrintNewLine:
    li $v0, 4
    la $a0, __PNL_newline
    syscall
    jr $ra
.data
    __PNL_newline: .asciiz "\n"

# subprogram:     PrintInt
# author:         Charles W. Kann
# purpose:        To print a string to the console
# input:          $a0 - The address of the string to print.
#                 $a1 - The value of the int to print
# returns:        None
# side effects:   The String is printed followed by the integer value.
.text
PrintInt:
    # Print string. The string address is already in $a0
    li $v0, 4
    syscall
    
    # Print integer. The integer value is in $a1, and must
    # be first moved to $a0.
    move $a0, $a1
    li $v0, 1
    syscall
    
    #return
    jr $ra

# subprogram:     PrintString
# author:         Charles W. Kann
# purpose:        To print a string to the console
# input:          $a0 - The address of the string to print.
# returns:        None
# side effects:   The String is printed to the console.
.text
PrintString:
    addi $v0, $zero, 4
    syscall
    jr $ra

# subprogram:     Exit
# author:         Charles Kann
# purpose:        to use syscall service 10 to exit a program
# input:          None
# output:         None
# side effects:   The program is exited
.text
Exit:
    li $v0, 10
    syscall