x86 Linux Assembly

add.asm

; NASM x86
global _start

_start:

mov eax, 2
mov edx, 1
add edx, eax   ; 3
add edx, '0'   ; '3'
mov [sum], edx

; write system call
mov eax, 4     ; write
mov ebx, 1     ; fd (STDOUT)
lea ecx, [sum] ; *buf
mov edx, 1     ; count (1 byte)
int 0x80

; exit system call
mov eax, 1 ; exit
mov ebx, 0 ; status (0)
int 0x80

section .bss
sum resb 1