Design a calculator in assembly that can handle +,-,/,%, * and expresses errors in the case of division by zero or invalid characters using the template below.

TITLE MASM Template (main.asm)

; Description: Calculator

; Revision date: April 29, 2014

INCLUDE Irvine32.inc

ENTER_KEY = 13

.data

prompt BYTE "Calculator: Enter an expression", 0dh, 0ah, 0

variableA dWord ?

variableB dWord ?

Problem BYTE "You cannot divide by 0",0dh,0ah,0

.code

calc_add PROC USES eax

mov eax, variableB

add variableA, eax

jno done

; display error

done:

ret

calc_add ENDP

calc_sub PROC

ret

calc_sub ENDP

calc_mul PROC

ret

calc_mul ENDP

calc_div PROC

; check divid by zero, remember to use cdq

ret

calc_div ENDP

calc_rem PROC

; check divid by zero, remember to use cdq

ret

calc_rem ENDP

main PROC

call Clrscr

mov ecx, OFFSET prompt

call WriteString ;print out: "Calculator: Enter an expression"

call Crlf ; new line

;read in the first number StateA: ;read in one digit at a time, continue reading until get a sign

mov eax, 0

call ReadChar

call IsDigit ;check to see if the value entered was a digit

jnz Error

sub al, '0'

mov variableA, eax

jmp StateB

StateB:

mov eax, 0

call ReadChar

cmp al, '+'

jnz L1

mov edx, calc_add

jmp StateC

cmp al, '-'

jnz L1:

mov edx, calc_sub

jmp StateC

; fill up the rest three operators

L1:

call IsDigit ;check to see if the value entered was a digit

jnz Error

sub al, '0'

mov ebx, eax

mov eax, 10

imul variableA

jo Error

mov variableA, eax ;

add variableA, ebx ; variableA = variableA * 10 + ebx

jmp StateB

StateC:

; similar to StateA

StateD:

; similar to StateB, except looking for ENTER

mov eax, 0

call ReadChar

cmp al, ENTER_KEY

jz Done

call isDigit

jnz Error

; fill up this part and compute variableB

jmp StateD

Done:

call edx

; display the result reading WriteInt

exit

main ENDP

END main