add_and_sub.asm

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

segment .data
    msg1 db "Enter a digit ", 0xa, 0xd
    len1 equ $- msg1

    msg2 db "Please enter a second digit ", 0xa, 0xd
    len2 equ $- msg2

    msg3 db "The sum is: "
    len3 equ $- msg3

segment .bss
    num1 resb 2
    num2 resb 2
    res resb 3

section .text
    global _start

_start:
    mov eax, SYS_WRITE
    mov ebx, STDOUT
    mov ecx, msg1
    mov edx, len1
    int 0x80

    mov eax, SYS_READ
    mov ebx, STDIN
    mov ecx, num1
    mov edx, 2
    int 0x80

    mov eax, SYS_WRITE
    mov ebx, STDOUT
    mov ecx, msg2
    mov edx, len2
    int 0x80

    mov eax, SYS_READ
    mov ebx, STDIN
    mov ecx, num2
    mov edx, 2
    int 0x80

    mov eax, SYS_WRITE
    mov ebx, STDOUT
    mov ecx, msg3
    mov edx, len3
    int 0x80

    ; moving the first number to eax register and the second to ebx
    ; and subtract ascii '0' to convert it into a decimal number

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

    mov ebx, [num2]
    sub ebx, '0'

    ; add eax and ebx
    add eax, ebx
    ; add ascii '0' to convert the sum from decimal to ascii
    add eax, '0'

    ;storing the sum in memory location res
    mov [res], eax

    ;print the sum
    mov eax, SYS_WRITE
    mov ebx, STDOUT
    mov ecx, res
    mov edx, 3
    int 0x80

exit:
    mov eax, SYS_EXIT
    xor ebx, ebx
    int 0x80