; lab.asm Program prints result of (Num^2) % Dig submitted by the client
;
    .MODEL SMALL
    .STACK 100h
    .DATA
Num          DW ?
Dig          DW ?
Remainder    DB ?
Ten          DW 10
PromptStr    DB 'Please Enter Number (from 00 up to 99):',13,10,'$'
PromptStr2   DB 13,10,'Please Enter Digit (from 0 up to 9):',13,10,'$'
ResultStr    DB 13,10,'XX^2 mod X = ',13,10,'$'
RoundUpStr   DB 13,10,'The result should be round up',13,10,'$'
RoundDownStr DB 13,10,'The result should be round down',13,10,'$'
DivErrorStr  DB 13,10,'Division error',13,10,'$'

    .CODE
    MOV AX,@DATA             ; DS can be written to only through a register
    MOV DS,AX                ; Set DS to point to data segment
    MOV AH,9                 ; Set print option for int 21h
    MOV DX,OFFSET PromptStr  ;  Set  DS:DX to point to PromptString
    INT 21h                  ;  Print PromptString
;       Read first digit of number
    MOV Num,0
    MOV AH,1
    INT 21h
    MOV ResultStr[2],AL
    SUB AL,'0'
    MOV AH,0
    MUL Ten
    MOV Num,AX
;       Read second digit of number
    MOV AH,1
    INT 21h
    MOV ResultStr[3],AL
    SUB AL,'0'
    MOV AH,0
    ADD Num, AX
;
    MOV AH,9                  ;  Set print option for int 21h
    MOV DX,OFFSET PromptStr2  ;  Set  DS:DX to point to PromptString2
    INT 21h                   ;  Print PromptString2
;       Read Dig
    MOV Dig, 0
    MOV AH,1
    INT 21h
    MOV ResultStr[11],AL
    SUB AL,'0'
    MOV AH,0
    ADD Dig, AX
;       Check Dig if ZERO
    CMP Dig, 0
    JE  DivisionError
;       Power Num by 2
    MOV AX,[Num]
    MUL [Num]
;       Do Modulo by division
    DIV [Dig]
    ADD Remainder, DL
    ADD DL,'0'
    MOV ResultStr[15],DL       ; Moves result to ResultStr
;       Print Result of calculations
    MOV AH,9
    MOV DX,OFFSET ResultStr
    INT 21h
;       Divides Dig by 2 and compares with Remainder
    MOV AX,[Dig]
    MOV BL,2
    DIV BL                      ; Divide Dig by 2
    CMP Remainder,AL            ; Compare Remainder with Dig/2
    JGE RoundUp                 ; If greater/equal print RoundUp
;       Otherwise, print RoundDown Message
    MOV AH,9
    MOV DX,OFFSET RoundDownStr
    JMP TerminateProg
;
RoundUp:
    MOV AH,9
    MOV DX,OFFSET RoundUpStr
    JMP TerminateProg

;       Print division by 0 error
DivisionError:
    MOV AH,9
    MOV DX,OFFSET DivErrorStr
;       Terminate program
TerminateProg:
    INT 21h
    MOV AH,4Ch                  ; Set terminate option for int 21h
    INT 21h                     ; Return to DOS (terminate program)
    END