3.3: Prompting for an Input Integer Number

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The next program, printInt, shows how to use scanf to read an input integer number from a user and then how to output that number back to the user using printf. It is contained in the following example program.

#
# Program Name:   printIntMain
# Author: Charles Kann
# Date:     9/19/2020
# Purpose: Uses scanf for an integer using data memory
# Input:
#   - input: User entered number
# Output:
#   - format: Prints the number
#

.text
.global main

main:
    # Save return to os on stack
    SUB sp, sp, #4
    STR lr, [sp, #0]    
    
    # Prompt for an input
    LDR r0, =prompt
    BL  printf    
    
    # Scanf
    LDR r0, =input
    LDR r1, =num
    BL scanf    
    
    # Printing the message
    LDR r0, =format
    LDR r1, =num
    LDR r1, [r1, #0]
    BL printf    
    
    # Return to the OS
    LDR lr, [sp, #0]
    ADD sp, sp, #4
    MOV pc, lr

.data
    # Allocates space for a word-aligned 4-byte value in the memory
    num: .word 0
    # Prompt the user to enter a number
    prompt: .asciz "Enter A Number\n"
    # Format of the user input, %d means integer number
    input: .asciz "%d"
    # Format to print the entered number
    format: .asciz "Your Number Is %d \n"

5 printIntMain

all: helloWorld printName printInt
helloWorld: helloWorldMain.s
      gcc $@Main.s -g -o $@      
      ./helloWorld
printName: printNameMain.s      
      gcc $@Main.s -g -o $@      
      ./printName
printInt:      
      gcc $@Main.s -g -o $@
      ./printInt

6 makefile for printInt