Question

I’m starting to learn assembly language. The program I need to do is very simple.
1 – Read a 4-digit number (can be a negative number)
2 – Output the number the entered number
3 – Calculate/Output the half of the entered number
4 – Calculate/Output the double of the entered number

So… this is the code… first, the data section

section .data ; Data segment
    msgPrompt       db 'Please enter a number ' ; Ask the user to enter a number
    lenMsgPrompt    equ $-msgPrompt          ; The length of the message
    msgNumber       db 'The entered number is '
    lenMsgNumber    equ $-msgNumber                 
    msgHalf         db 'The half of the entered number is '
    lenMsgHalf      equ $-msgHalf
    msgDouble       db 'The double of the entered numbered is '
    lenMsgDouble    equ $-msgDouble

Then the uninitialized data (for the user input)

section .bss        ; Uninitialized data
    userNumber    resb 5
    halfNumber    resb 5
    doubleNumber  resb 5

Then… the code segment…

    section .text       ; Code Segment

       global _start
       _start:

       ;Prompt the user
       mov eax, 4
       mov ebx, 1
       mov ecx, msgPrompt
       mov edx, lenMsgPrompt
       int 80h

       ; Read and store the user input
       mov eax, 3
       mov ebx, 2
       mov ecx, userNumber  
       mov edx, 5       ; 5 bytes (numeric, 1 for sign) of that information
       int 80h

       ; Output the message 'The entered number is '
       mov eax, 4
       mov ebx, 1
       mov ecx, msgNumber
       mov edx, lenMsgNumber
       int 80h  

       ; Output the number entered
       mov eax, 4
       mov ebx, 1
       mov ecx, userNumber
       mov edx, 5
       int 80h  

       ; Output the message 'The half of the entered number is '
       mov eax, 4   
       mov ebx, 1
       mov ecx, msgHalf
       mov edx, lenMsgHalf
       int 80h

       ; Calculate the half of the number entered
       mov eax, [userNumber]
       shr eax, 1       ; Shift to the right by one bit
       mov [halfNumber], eax

       ; Output half of the number entered
       mov eax, 4
       mov ebx, 1
       mov ecx, halfNumber
       mov edx, 5
       int 80h

       ; Output the message 'The double of the entered numbered is '
       mov eax, 4
       mov ebx, 1
       mov ecx, msgDouble
       mov edx, lenMsgDouble
       int 80h

       ; Calculate the double of the number entered
       mov ebx, [userNumber]
       shl ebx, 1       ; Shift the the left by one bit
       mov [doubleNumber], ebx

       ; Output double of the number entered
       mov eax, 4
       mov ebx, 1
       mov ecx, doubleNumber
       mov edx, 5
       int 80h

       ; Leave program
       mov eax, 1
       mov ebx, 0
       int 0x80

This is the final result… Here (I don’t have enough reputation yet to post images…)

As you can see, there is problem… Also, I would like to have a new line after ‘The half of the number is xxxxx’.

Thank you

Answer 1

Looks like you’re doing arithmetic on ASCII codes for the digits, instead of the numeric value.