Okay... One thing I didn't notice at first which caused me quite a bit of trouble: your choice message says 3 is div and 4 is mul, but the code jumped to _mul on 3 and _div on 4. The user (me) is carefully selecting inputs that will give a single-digit result, and it isn't working right. Duh!
Well, I think I've got it working for single digits (and positive, in the case of "sub"). I changed the code to match the message - probably would be better to change the message(?). This is what I've got, at present:
SYS_EXIT equ 1
SYS_READ equ 3
SYS_WRITE equ 4
STDIN equ 0
STDOUT equ 1
segment .data
msg1 db "Enter the first digit", 0xA,0xD
len1 equ $- msg1
msg2 db "Please enter a second digit", 0xA,0xD
len2 equ $- msg2
msg3 db "Enter a choice 1 ADD 2 = SUB 3 = DIV 4 =MUL ", 0xA,0xD
len3 equ $- msg3
msg5 db 10,'Invalid Option',10,0
len5 equ $ - msg5
msg6 db "Operation: ",0
len6 equ $ - msg6
msg4 db "The sum is: ",10
len4 equ $- msg4
nline db 10,0
lnline equ $ - nline
segment .bss
choice resb 2
num1 resb 2
num2 resb 2
res resb 2
section .text
global _start
_start: ;tell linker entry point
mov eax, SYS_WRITE ;"Enter the first digit", 0xA,0xD
mov ebx, STDOUT
mov ecx, msg1
mov edx, len1
int 0x80
mov eax, SYS_READ ; read the 1st Digit entered by the user
mov ebx, STDIN
mov ecx, num1
mov edx, 2
int 0x80
mov eax, SYS_WRITE ;"Please enter the second digit", 0xA,0xD
mov ebx, STDOUT
mov ecx, msg2
mov edx, len2
int 0x80
mov eax, SYS_READ ; read 2nd user input
mov ebx, STDIN
mov ecx, num2
mov edx, 2
int 0x80
mov eax, SYS_WRITE ; "Enter a choice 1 ADD 2 = SUB 3 = DIV 4 =MUL ",
mov ebx, STDOUT
mov ecx, msg3
mov edx, len3
int 0x80
; Print on screen the message 8: operation
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg6
mov edx, len6
int 80h
; We get the option selected: any one from 1,2,3,4
mov ebx,STDIN
mov ecx,choice
mov edx,2
mov eax, SYS_READ
int 80h
mov ah, [choice] ; move the users choice into ah register
sub ah,'0'
cmp ah, 1 ; compare user choice with the available options
je _ADD ;if choice == 1 jump to add label
cmp ah, 2
je _SUB
cmp ah, 4
je _MUL
cmp ah, 3
je _DIV
mov eax, SYS_WRITE ; if the wrong choice is entered
mov ebx, STDOUT
mov ecx, msg5
mov edx, len5
int 0x80
jmp exit
_printMsg4:
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, msg4
mov edx, len4
int 80h
jmp _printSum
; print the sum
_printSum:
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, res ; print the value of sum on the screen
mov edx, 2
int 0x80
jmp exit ; jump to exit the program
; moving the first number to eax register and second number to ebx
; and subtracting ascii '0' to convert it into a decimal number
_ADD:
mov al, [num1]
sub al, '0'
mov bl, [num2]
sub bl, '0'
add al, bl ; al and bl
add al, '0' ; add '0' to to convert the sum from decimal to ASCII
mov [res], al ; storing the sum in memory location
int 80h
jmp _printMsg4
_SUB:
mov al, [num1]
sub al, '0'
mov bl, [num2]
sub bl, '0'
sub al, bl ; al and bl
add al, '0' ; add '0' to to convert the sum from decimal to ASCII
mov [res], al ; storing the sum in memory location
int 80h
jmp _printMsg4
_DIV:
; We store the numbers in registers ax and bx
mov al, [num1]
sub al, '0' ; Convert from ascii to decimall
mov bl, [num2]
sub bl, '0'
mov ah, 0 ;remainder
; mov eax, 0 ;quotient
; Division. Ax = AX / BX
div bl
; Conversion from decimal to ascii
add al, '0'
; We move the result
mov [res], al
; int 80h
jmp _printMsg4
_MUL:
; We store the numbers in registers al and bl
mov al, [num1]
mov bl, [num2]
; Convert from ascii to decimal
sub al, '0'
sub bl, '0'
; Multiply. AX = AL x BL
mul bl
; Conversion from decimal to ascii
add al, '0'
; We move the result
mov [res], al
; int 80h
jmp _printMsg4
exit:
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, nline
mov edx, lnline
int 80h
mov eax, SYS_EXIT
mov ebx,0
int 80h
If I get to it, I'll post a version that will handle multiple digits (positive and negative?). Maybe I'll go through it and pick a few nits - stuff that's not exactly an "error", but not really right - carriage returns, for example...
Later,
Frank
