; Macro for printing messages

printmsg macro msg
         push ax
         push bx
         push cx
         push dx
         LEA dx,msg
         mov ah,09h
         int 21h
         pop dx
         pop cx
         pop bx
         pop ax
endm    

; begins data segment
.data
        
        
                       
        msg1 db 0ah,0dh,"Enter first number  NUM1= $"
        msg2 db 0ah,0dh,"Enter second number NUM2= $"
        msg3 db 0ah,0dh,"1=> Addition 2=>Substraction 3=>Multiplication  4=>Division:  $"
        msg4 db 0ah,0dh,"Enter your option :  $"
        msg10 db 0ah,0dh," $"
        msg5 db 0ah,0dh," NUM1 + NUM2 = $"
        msg6 db 0ah,0dh," NUM1 - NUM2 = $"
        msg7 db 0ah,0dh," NUM1 * NUM2 = $"
        msg8 db 0ah,0dh," NUM1 / NUM2 = $"
        msg9 db 0ah,0dh,"NO SUCH OPTION $"
        num dw 0
        cnt dw 0
        choice dw 0
        a dw 0
        b dw 0

        output dw 0
      
       
 ; begins code segment      

.code
        mov ax,@data    ; code segment get the address of data segment of this program
        mov ds,ax
        printmsg msg1   ; Print the message in msg1 of data segemnt
        call readnum    ; Use procedure to read the number
        mov ax,num      ; Store this number in ax register
        mov a,ax
        printmsg msg10  ; printing a new line
        printmsg msg2
        call readnum
        mov bx,num
        mov b,bx
        printmsg msg3  ; printing menu
   loop1:
        printmsg msg10  ; printing a new line
        printmsg msg4
                
        call readnum
        mov ax,num
        mov choice,ax
        cmp choice,01
        je addi
        cmp choice,02
        je subt
        cmp choice,03
        je multi
        cmp choice,04
        je divi 
        printmsg msg10  ; printing a new line
        printmsg msg9
        call printnum
        jmp ex

  addi:  
        printmsg msg10  ; printing a new line
        printmsg msg5  ; Print the message in msg5
        mov ax,a       ; move the NUM1 to ax register 
        add ax,b       ; add the ax register with NUM2 whish is in varisble  b and the result will be in ax register
        mov num,ax     ; Moving this to varaible num for printing
        call printnum  ; call the print procedure for printing. 
        jmp loop1
  subt:
        printmsg msg10  ; printing a new line
        printmsg msg6
        mov ax,a
        mov bx,b
        sub ax,bx
        mov num,ax
        call printnum
        jmp loop1
  multi: 
        printmsg msg10  ; printing a new line
        printmsg msg7
        mov ax,a
        mov bx,b
        mul bx         ; Multilying with ax register will give ax*bx  and the result will be in ax register.
        mov num,ax     ; 
        call printnum
        jmp loop1
   divi:
        printmsg msg10  ; printing a new line
        printmsg msg8
        mov ax,a
        mov bx,b
        XOR dx,dx     ; clearing dx register for storing higher order bits if any after multiplication
        div bx
        mov num,ax
        call printnum
        jmp ex

        
   ex:                   ; Interrruot to exit to the dos
        mov ah,4ch
        int 21h  
 
 ; Procedure to read a number to the variable num declared in the data segment

readnum proc near
                push ax
                push bx
                push cx
                push dx
                mov num,00
           r1:
               mov ah,01h
               int 21h
               cmp al,0dh
               je r2
               mov cx,ax
               and cx,00ffh
               sub cx,30h
               mov bx,10
               mov ax,num
               mul bx
               add ax,cx
               mov num,ax
               jmp r1
           r2:
               pop dx
               pop cx
               pop bx
               pop ax
           ret
readnum endp  

; Procedure to print a number to the variable num declared in the data segment

printnum proc near
                push ax
                push bx
                push cx
                push dx
                mov ax,num
                mov bx,10
          p1:
                mov dx,00
                div bx
                push dx
                inc cnt
                cmp ax,00
                jne p1
          p2:
                cmp cnt,00
                je p3
                pop dx
                add dl,30h
                mov ah,02h
                int 21h
                dec cnt
                jmp p2
          p3:
                pop dx
                pop cx
                pop bx
                pop ax
               
          ret
  printnum endp
end