demo-calc.asm

SYS_EXIT  equ 1
SYS_READ  equ 3
SYS_WRITE equ 4
STDIN     equ 0
STDOUT    equ 1


section .data           ; initialized data, messages

    welcome     db      'Welcome to the Calculator',10,0
    input1      db      'Enter first number:',0
    input2      db      'Enter second number:',0
    operators   db  '1. +', 10
        db  '2. -', 10
        db  '3. *', 10
        db  '4. /', 10, 0
    choice      db      'Your choice is: ',10,0
    outcome     db      'and the Result is: ',0
    error       db      'SORRY, Wrong choice!',10,0

    nlinea      db      10,0

section .bss            ;uninitialized data
; Spaces reserved for storing the values provided by the user.

    opc:        resb    2      ;reserves 2 byte in binary
    num1:       resb    2
    num2:       resb    2
    result:     resb    2

section .text           ;asm code

    global _start         ;must be declared for using gcc

_start:
    jmp main

; printstr  print ascii string, which terminate with 0 byte
; input
;   eax - point to begining of string
; return
;   nothing
printstr:
    push    eax
    push    ebx
    push    ecx
    push    edx
    push    esi

    mov ecx, eax    ; we store address of string in eax
    mov eax, SYS_WRITE
    mov ebx, STDOUT
    mov esi, ecx    ; looking for end of stringS
    mov edx, 0
.0:
    cmp byte [esi], 0
    je  .1
    inc edx
    inc esi
    jmp .0
.1:
    int 0x80
    pop esi
    pop edx
    pop ecx
    pop ebx
    pop eax
    ret

; myexit    terminate program
; input
;   nothing
; output
;   nothing
myexit:
    mov eax, 1
    mov ebx, 0
    int 0x80


; main function start here!
main:
    mov eax, welcome
    call    printstr
    mov eax, input1
    call    printstr

    ; We get num1 value for first number.
    mov eax, 3
    mov ebx, 0
    mov ecx, num1
    mov edx, 2
    int 80h

    mov eax, input2
    call    printstr

    ; We get num2 value for second number.
    mov eax, 3
    mov ebx, 0
    mov ecx, num2
    mov edx, 2
    int 80h
    mov al,[num2]
    sub al, '0'
    mov [num2],al

    mov al,[num1]
    sub al, '0'
    mov [num1],al

    mov eax, operators
    call    printstr

    mov eax, choice
    call    printstr

    ; Shows our choice
    mov eax,3
    mov ebx,0
    mov ecx,opc
    mov edx,2
    int 80h

    mov ah, [opc]   ; Move our choice to the 8bit ah register
    sub ah, '0'     ; Convert from ascii to decimal



    ; We compare the value entered by the user to know what operation to perform.
    ; Basically, it is IF function (cmp)
    cmp ah, 1
    je addition         ;jump equal or jump zero
    cmp ah, 2
    je subtraction
    cmp ah, 3
    je multiplication
    cmp ah, 4
    je division




    ; If the user choose wrong choice, it will show error and close porgram
    mov eax, error
    call printstr
    call myexit

addition:
    ; We keep the numbers in the 8bit al and bl registers
    mov al, [num1]
    mov bl, [num2]

    ; Converts from ascii to decimal
    ;sub al, '0'
    ;sub bl, '0'

    ; Addition
    add al, bl

    ; Again converts from decimal to ascii
    add al, '0'

    ; We move the result
    mov [result], al



    ; We end our program
    jmp exit

subtraction:
    ; We keep the numbers in 8bit al and bl registers
    mov al, [num1]
    mov bl, [num2]

    ; Convert from ascii to decimal
    ;sub al, '0'
    ;sub bl, '0'

    ; Subtraction
    sub al, bl

    ; Again converts from decimal to ascii
    add al, '0'

    ; We move the result
    mov [result], al



    ; We end our program
    jmp exit

multiplication:

    ; We keep the numbers in 8bit al and bl registers
    mov al, [num1]
    mov bl, [num2]

    ; Convert from ascii to decimal
    ;sub al, '0'
    ;sub bl, '0'

    ; Multiplication. AX = AL x BL
    mul bl

    ; Again converts from decimal to ascii
    add ax, '0'

    ; We move the result
    mov [result], ax



    ; We end our program
    jmp exit

division:

    ; We keep the numbers in 8bit al and bl registers
    mov al, [num1]
    mov bl, [num2]

    mov dx, 0
    mov ah, 0

    ; Convert from ascii to decimall
    ;sub al, '0'
    ;sub bl, '0'

    ; Division. AL = AX / BX
    div bl

    ; Again converts from decimal to ascii
    add ax, '0'

    ; We move the result
    mov [result], ax



    ; We end our program
    jmp exit

exit:

; Prints 'and the Result is: '
    mov eax, outcome
    call printstr

    ; Prints outcome
    mov eax, 4
    mov ebx, 1
    mov ecx, result
    mov edx, 1
    int 80h
    ; Prints on screen two new lines
    mov eax, 4
    mov ebx, 1
    mov ecx, nlinea
    ; mov edx, lnlinea
    int 80h

    ; We end our program
    mov eax, 1
    mov ebx, 0
    int 80h