model tiny
STACK 256
DATASEG
  mes1 db '1. Suma',0dh,0ah,'$'
  mes2 db '2. Riznyzja',0dh,0ah,'$'
  mes3 db '3. Dobutok',0dh,0ah,'$'
  mes4 db '4. Chastka',0dh,0ah,'$'
  info db 'Vyberit variant',0dh,0ah,'$'
  lol db 'Input Error!',0dh,0ah,'$'
  info2 db 'Vvedit pershe chuslo',0dh,0ah,'$'
  info3 db 'Vvedit druge chuslo',0dh,0ah,'$'
  errormes db 'incorrect number',0dh,0ah,'$'
  buff db 6,7 Dup(?)
CODESEG
 start:
         mov ax,@data
         mov ds,ax

         mov dx,offset mes1
         mov ah,09h
         int 21h
         mov dx,offset mes2
         mov ah,09h
         int 21h
         mov dx,offset mes3
         mov ah,09h
         int 21h
         mov dx,offset mes4
         mov ah,09h
         int 21h
         mov dx,offset info
         mov ah,09h
         int 21h

    CALL InputInt


         cmp ax,1
         je suma
         cmp ax,2
         je rizn
         cmp ax,3
         je dobutok
         cmp ax,4
         je chastka
         jmp error

   suma:
         lea dx,info2
         mov ah,09h
         int 21h

   CALL InputInt

         mov bx,ax
         mov dx,offset info3
         mov ah,09h
         int 21h
   CALL InputInt
         add ax,bx
         jmp kinez

   rizn: mov dx,offset info2
         mov ah,09h
         int 21h

   CALL InputInt

         mov bx,ax
         mov dx,offset info3
         mov ah,09h
         int 21h
   CALL InputInt
         sub ax,bx
         jmp kinez

dobutok: mov dx,offset info2
         mov ah,09h
         int 21h

   CALL InputInt

         mov bx,ax
         mov dx,offset info3
         mov ah,09h
         int 21h
   CALL InputInt
         mul bx
         jmp kinez

chastka: mov dx,offset info2
         mov ah,09h
         int 21h

   CALL InputInt

         mov bx,ax
         mov dx,offset info3
         mov ah,09h
         int 21h
   CALL InputInt
         xor dx,dx
         div bx
         jmp kinez

  error: mov dx,offset lol
         mov ah,09h
         int 21h
   CALL InputInt
         xor ah,ah
         int 16h
  kinez:
       CALL OutputInt
         xor ah,ah
         int 16h
         mov ah,04Ch
         mov al,1h
         int 21h
InputInt proc
         push bx
         mov ah,0ah
         xor di,di
         mov dx,offset buff
         int 21h
         mov ah,02h
         int 21h

         mov si,offset buff+2
         cmp byte ptr [si],"-"
         jnz ii1
         mov di,1
         inc si

ii1:     xor ax,ax
         mov bx,10
ii2:     mov cl,[si]
         cmp cl,0dh
         jz endin
         cmp cl,'0'
         jl er
         cmp cl,'9'
         ja er
         sub cl,'0'
         mul bx
         add ax,cx
         inc si
         jmp ii2
er:
         mov dx,offset errormes
         mov ah,09h
         int 21h
         int 20h
endin:
         cmp di,1
         jnz ii3
         neg ax
ii3:
         pop bx
         ret
InputInt endp
OutputInt proc
         test ax,ax
         jns oi1
         mov cx,ax
         mov ah,02h
         mov dl,'-'
         int 21h
         mov ax,cx
         neg ax
oi1:
         xor cx,cx
         mov bx,10
oi2:
         xor dx,dx
         div bx
         push dx
         inc cx
         test ax,ax
         jnz oi2
         mov ah,02h
oi3:
         pop dx
         cmp dl,9
         jbe oi4
         add dl,7
oi4:
         add dl,'0'
         int 21h
         loop oi3
ret
OutputInt endp
END start