STSEG SEGMENT PARA STACK "STACK"
DB 64 DUP("STACK")
STSEG ENDS

DSEG SEGMENT PARA PUBLIC "DATA"

HELLO_MESSAGE DB 'Input number [-32767..32767]: ',13,10,'$'
OUTPUT_MESSAGE DB "You've entered number: ",'$'
BAD_INPUT DB 'Incorrect input!',13,10,'$'
INPUT DB 7,?,8 DUP('$')
IS_NEGATIVE DB 1 DUP('0')
DSEG ENDS

CSEG SEGMENT PARA PUBLIC "CODE"
MAIN PROC FAR
ASSUME SS:STSEG, DS: DSEG,CS:CSEG
PUSH DS
XOR AX, AX
PUSH AX
MOV AX, DSEG
MOV DS, AX
CALL INPUT_NUMBER
CALL OUTPUT_NUMBER
RET
MAIN ENDP


INPUT_NUMBER PROC NEAR

; write message
MOV AH, 9
LEA DX, HELLO_MESSAGE
INT 21H

;read line
LEA DX, INPUT
MOV AH, 10
INT 21H

MOV DI, offset INPUT+2 ; DI - POINTER TO THIRD ELEMENT OF INPUT
CMP BYTE PTR [DI], '-' ;
JE NEGATIVE            ; IF [DI] == '-' GOTO NEGATIVE
CMP BYTE PTR [DI],'+'
JE POSITIVE

LABEL1:
   XOR BX,BX    ; BX=0000
   MOV BX,10
   XOR AX,AX

LABEL2:
   XOR CX,CX
   CMP BYTE PTR [DI], 0DH    ; ODH - END STRING
   JZ LABEL5
   CMP BYTE PTR [DI], 30H    ; IF <30 - NOT A NUMBER
   JB BAD_NUMBER
   CMP BYTE PTR [DI], 39H    ; IF >39 - NOT A NUMBER
   JA BAD_NUMBER
   MOV CL, [DI]
   SUB CL, 30H               ; CONVERT TO NUMBER 0..9
   MUL BX                    ; MUL BL AND AL, RESULT IN AX
   JC BAD_NUMBER             ; JUMP IF CARRY FLAG (WE HAVE OVERFLOW)
   ADD AX,CX
   JC BAD_NUMBER
   INC DI
   JMP LABEL2
NEGATIVE:                  ; SET IS_NEGATIVE 1
   PUSH AX
   MOV AL, IS_NEGATIVE
   MOV AL, 1
   MOV IS_NEGATIVE, AL
   POP AX
   INC DI
   JMP LABEL1
POSITIVE:
   PUSH AX
   MOV AL, 0
   MOV IS_NEGATIVE, AL
   POP AX
   INC DI
   JMP LABEL1
BAD_NUMBER:              ;ERROR OR BAD NUMBER
   MOV AH, 9
   LEA DX, BAD_INPUT
   INT 21H
   MOV AH, 1 ; GETCH() WAIT FOR USER (READING MESSAGE)
   INT 21H
   MOV AH, 4CH ; EXIT() IN C
   INT 21H
LABEL5:
   CMP AX, 32767
   JA BAD_NUMBER
   MOV CL, IS_NEGATIVE
   CMP CL, 1
   JNZ L6
   NEG AX
L6:   RET
INPUT_NUMBER ENDP

OUTPUT_NUMBER PROC NEAR


MOV CX, AX ; MOVE OUR NUMBER TO CX -> USING INT

; write message
MOV AH, 9
LEA DX, OUTPUT_MESSAGE
INT 21H

MOV AX,CX ; MOVE OUR NUMBER BACK TO AX
MOV BL, IS_NEGATIVE ; IF IS_NEGATIVE = 1 -> OUR NUMBER NEGATIVE -> OUTPUT '-'
CMP BL, 1
JNZ POS
MOV AH,2  ; OUTPUT CHAR
MOV DL, '-'
INT 21H
MOV AX,CX
NEG AX
POS:
   XOR CX,CX ;CX = 0
   XOR BX,BX
   MOV BX,10 ;BL=10
L1:
   XOR DX,DX
   DIV BX   ; AX DIVIDE BX RESULT DX
   PUSH DX  ; PUSH DIGIT TO STACK
   INC CX   ; INC COUNTER OF DIGITS

   TEST AX,AX ; IF AX = 0, ZF = 1
   JNZ L1
   MOV AH,2 ;
L2:
   POP DX ; BRING OUR DIGIT
   ADD DL, 30H ; ADD 30 OR '0' TO CONVERT NUMBER TO CHAR
   INT 21H
   LOOP L2 ; CX = NUMBER OF DIGITS EVERY LOOP DEC CX. IF CX=0 LOOP ENDS
RET
OUTPUT_NUMBER ENDP

CSEG ENDS
END MAIN