Assembly : add two numbers

Question

I would like to add two number num1B and num2B and store the number in result, finaly show result.

But, when i launch nasm, it says :

prog2_1.txt:4: warning: attempt to initialize memory in a nobits section: ignored

prog2_1.txt:5: warning: attempt to initialize memory in a nobits section: ignored

prog2_1.txt:6: warning: attempt to initialize memory in a nobits section: ignored

my code :

org 0x0100 ;

section .bss
    num1B: db 0Ah ; init num1B to 0Ah
    num2B: db 00111111b ; init num2B to 00111111b
    result: db 0 ; init result to 0

section .data

section .text

    mov AX,0 ; AX = 0
    add AX,[num1B] ; AX = AX + num1B
    add AX,[num2B] ; AX = AX + num2B
    mov [result],AX ; result = result + AX

    mov DX,[result] ; show result
    mov AH,09h
    int 21h

    mov AH,4Ch
    int 21h

Thank you

Answer 1

You need to change your .bss section to .data section. The .bss section is meant for uninitialized data, while the .data section is meant for initialized data. That's why you can't use db, dw and so forth in .bss section. Instead, you can place them in .data section. Similarly, you can use resb. resw and so forth in .bss section but not in .data section.

In short, .data is for initialized data and .bss is for uninitialized data.

Answer 2

You're right, it's a long road. If you want "easy", stick to BASIC! You're making progress. You've got your two numbers in ".data", not ".bss", but I assume they're still "db". When you use ax for the addition, it uses 16 bits - a "word" or two bytes. This puts one number in al and the second number in ah - not what you want! Either use al for the addition, or make your two numbers (and the result!) "dw" rather than "db". "Display the result" is the hard part, and doing words is probably easier than bytes, besides letting you display numbers bigger than 255. Someone has just posted a "display the result" routine... as a macro for Masm, but you should be able to modify the code to work in Nasm. You probably don't want a macro - it'll duplicate the same code every time you use it. A subroutine would be better, but if you don't know how to do that just put it "in line" - you're only doing it once (for now). If you continue to have trouble, post some more recent code...

Best, Frank http://www.nasm.us