Trying to compare input of ' ' with its ASCII value of 43-CodePudding

I'm new to writing posts with code imbedded in them so give me a break if this looks terrible, or suggestions on how to make it look nicer. :)

The issue I'm having is pretty much what the title says. I am making a simple calculator for an assignment, I am trying to have the program compare an inputted math operation such as ( ,-,*,/).

*Then have a cmp set up something like....

cmp MathOper, 43...*

*But I am having troubles getting the program to recognize the right thing. I'll post a copy of the code below, but keep in mind this is a rough draft just trying to work out some ideas. *

Thanks for any and all help!

; Author:  
; Date:    03/22/2022

.586
.MODEL FLAT

INCLUDE io.h            ; header file for input/output

.STACK 4096

.DATA
num1                   DWORD    ?
num2                   DWORD    ?
MathOper               DWORD    ?
result                 DWORD    20 DUP (?), 0
string                 BYTE     40 DUP (?), 0




Num1prm       BYTE  "Enter First Number", 0
Num2prm       BYTE  "Enter Second Number", 0
MathOPprm     BYTE  "Enter Math Operation ( ,-,*,/)", 0
Resultprm     BYTE  "The Result is: ", 0
                            


.CODE
_MainProc PROC
loopy:
            input  Num1prm, string, 20
            atod    string
            mov     num1, eax
            
            input  MathOPprm, string, 20
            atod    string
            mov     MathOper, eax

            input  Num2prm, string, 20
            atod    string
            mov     num2, eax

            
            ;HAVING ISSUES GETTING THIS TO WORK
            cmp MathOper, 43
            jne SUBTRACTION
            call Addition
            dec ecx
            jnz loopy
           
           
           
            SUBTRACTION:           
            cmp MathOper, 45
            jne MULTIPLICATION
            call Subtraction

            MULTIPLICATION:
            cmp MathOper, 42
            jne DIVISION
            call Multiplication

            DIVISION:
            cmp MathOper, 47
            call Division
            cmp MathOper, 101
         
      
 endloopy:

            mov     eax, 0                   ; exit with return code 0
            ret
_MainProc ENDP
                                             ; end of source code


Addition PROC
        push    ebp
        mov     ebp, esp
        push    ebx
        
        mov     eax, num1
        mov     ebx, num2
        add     eax, ebx
        dtoa    result, eax

        output  Resultprm, result, 40
        pop     ebx
        pop     ebp

        ret
Addition ENDP

Subtraction PROC
        push    ebp
        mov     ebp, esp
        push    ebx
        
        mov     eax, num1
        mov     ebx, num2
        sub     eax, ebx
        dtoa    result, eax

        output  Resultprm, result, 40
        pop     ebx
        pop     ebp

        ret
Subtraction ENDP

Multiplication PROC
        push    ebp
        mov     ebp, esp
        push    ebx
        
        mov     eax, num1
        mov     ebx, num2
        mul     ebx
        dtoa    result, eax

        output  Resultprm, result, 40
        pop     ebx
        pop     ebp

        ret
Multiplication ENDP

Division PROC
        push    ebp
        mov     ebp, esp
        push    ebx
        
        mov     eax, num1
        mov     ebx, num2
        cdq
        idiv    ebx
        dtoa    result, eax

        output  Resultprm, result, 40
        pop     ebx
        pop     ebp

        ret
Division ENDP


END

CodePudding user response：

You don't want to call atod on string after reading the input, because it isn't a number.
Just copy the first character of the string into MathOper using this:

    movzx eax, [string]
    mov MathOper, eax