;############## CALCULATOR ########################
DATA SEGMENT
    X DW 0,0
    Y DW 0,0
    BUF DW 0,0
    RESULT DW 0,0,0,0
    OUTSTRING DB 12 DUP(0) ;output string
    SIGN DB 0
    OPERATOR DB 0
    TAG DB ?           ;label for repeat or not
    FLAG DB 0          ;if(FLAG==0) then '0' will not be outputed
    DCB DW  17H,4876H,0E800H, 2H,540BH,0E400H, 0,3B9AH,0CA00H,0,5F5H,0E100H,0,98H,9680H,0,0FH,4240H,0,1H,86A0H,0,0,2710H,0,0,3E8H,0,0,64H,0,0,0AH,0,0,1H        
;   10^11,10^10,...,10,1 
    M1 DB 'PLEASE ENTER THE FIRST OPERAND: $'
    M2 DB 'PLEASE ENTER THE SECOND OPERAND: $'
    OPR DB 'PLEASE SECLECT OPERATOR 1)+ 2)- 3)* 4)/ : $'
    ERR DB 'INPUT ERROR!$ '
    RES DB 'RESULT IS: $'
    AGAIN DB 'WOULD YO LIKE TO DO AGAIN (Y/N)? $'
DATA ENDS
CODE SEGMENT
   ASSUME CS:CODE,DS:DATA
START:
MAIN    PROC FAR
	MOV AX,DATA
	MOV DS,AX
REPEAT:	MOV BX,10          
	MOV SIGN,0      ;sign of the result
	MOV TAG,0
        CALL INPUT1
	CALL INPUT2
	CALL SELECT     ;select operator
	MOV DL,13       ;next line
	MOV AH,02H
	INT 21H
	MOV DL,10
	MOV AH,02H
	INT 21H
	MOV AL,OPERATOR
	CMP AL,1
	JNZ  L0
	CALL A          ;add  
	JMP L3
L0:	CMP AL,2
	JNZ  L1
	CALL S          ;subtract
	JMP L3
L1:	CMP AL,3
	JNZ  L2
	CALL M          ;multiply
	JMP L3
L2:	CMP AL,4
	JNZ  L3
	CALL D          ;divided by
L3:	MOV DL,13       ;next line
	MOV AH,02H
	INT 21H
	MOV DL,10
	MOV AH,02H
	INT 21H
	CALL RE         ;ask if repeat
	MOV DL,13
	MOV AH,02H
	INT 21H
	MOV DL,10
	MOV AH,02H
	INT 21H
	MOV AL,TAG
	CMP AL,1
	JZ  REPEAT
	MOV AH,4CH      ;over
	INT 21H
MAIN    ENDP
;############### ENTER THE FIRST OPRAND ###################
INPUT1   PROC NEAR
  	MOV CX,6        ;for 6 bit of decimal most
  	MOV X,0         ;let x=0 in case calculation is doing for more than once
  	MOV X+2,0
	LEA DX,M1
	MOV AH,09H
	INT 21H
L4:  	MOV AH,01H
        INT 21H
        CMP AL,0DH      ;when receive 'enter' cease the input
        JZ L5
        SUB AL,30H      ;if (AL) < 0 , error
  	JC  NEXT1
  	CMP AL,0AH
  	JNC NEXT1       ;if (AL) >10,  error
  	MOV AH,0
  	MOV BUF,AX
  	MOV AX,X+2      ; x = x*10 + (Al)
  	MUL BX
  	MOV X+2,AX
  	MOV AX,X
	MOV DX,0
	MUL BX
	ADD AX,BUF
	MOV X,AX
	ADC X+2,DX
 	LOOP L4
	JMP L5
NEXT1:   LEA DX,ERR     ;error
	MOV AH,09H
	INT 21H
L5:	MOV DL,13       ;next line
	MOV AH,02H
	INT 21H
	MOV DL,10
	MOV AH,02H
	INT 21H
	RET
INPUT1 ENDP	
;################ ENTER THE SECOND OPERAND ####################### 	
INPUT2   PROC NEAR
  	MOV CX,6        ;for 6 bit of decimal most
  	MOV Y,0         ;let y=0 in case calculation is doing for more than once 
  	MOV Y+2,0
	LEA DX,M2
	MOV AH,09H
	INT 21H
L6:  	MOV AH,01H
        INT 21H
        CMP AL,0DH      ;when receive 'enter' cease the input
        JZ L7
        SUB AL,30H
  	JC  NEXT2
  	CMP AL,0AH
  	JNC NEXT2
  	MOV AH,0
  	MOV BUF,AX
  	MOV AX,Y+2
  	MUL BX
  	MOV Y+2,AX      ;much the same as 'INPUT1'
  	MOV AX,Y
	MOV DX,0
	MUL BX
	ADD AX,BUF
	MOV Y,AX
	ADC Y+2,DX
 	LOOP L6
	JMP L7
NEXT2:   LEA DX,ERR
	MOV AH,09H
	INT 21H
L7:	MOV DL,13
	MOV AH,02H
	INT 21H
	MOV DL,10
	MOV AH,02H
	INT 21H
	RET
INPUT2 ENDP
;################ SELECT OPRATOR #####################
SELECT PROC NEAR         ;select from 1 to 4
        LEA DX,OPR       ; 1----add
        MOV AH,09H       ; 2----subtract
        INT 21H          ; 3----multiply
        MOV AH,01H       ; 4----divided by
        INT 21H
        SUB AL,30H
        CMP AL,1
        JC  NEXT3
        CMP AL,5
        JNC NEXT3
        MOV OPERATOR,AL
        RET
NEXT3:  LEA DX,ERR
	MOV AH,09H
	INT 21H
	RET
SELECT ENDP
;#################### ADD ############################
A PROC NEAR
	MOV AX,X
	ADD AX,Y          ;simply add x and y
	MOV RESULT,AX     ;keep the result
	MOV AX,X+2
	ADC AX,Y+2
	MOV RESULT+2,AX
	LEA DX,RES        ;output
	MOV AH,09H
	INT 21H
	CALL OUTPUT1  
	RET
A ENDP
;############### SUBTRACT ############################
S PROC NEAR
	MOV AX,X+2
	CMP AX,Y+2        ;compare x and y
	JNBE  L8          ;if x >= y,  sign = 0, result = x - y
	JB  L9            ;if x < y,  sign = 1, result = y - x
	MOV AX,X          
	CMP AX,Y          
	JB  L9
L8:     MOV AX,X      
   	SUB AX,Y
   	MOV RESULT,AX
   	MOV AX,X+2
   	SBB AX,Y+2
   	MOV RESULT+2,AX
   	RET
   L9:  MOV SIGN,1        ;result is negative
   	MOV AX,Y
   	SUB AX,X
   	MOV RESULT,AX     ;keep the result
   	MOV AX,Y+2
   	SBB AX,X+2
   	MOV RESULT+2,AX
   	LEA DX,RES        ;output
	MOV AH,09H
	INT 21H
   	CALL OUTPUT1
   	RET
S ENDP
;############## MULTIPLY ##############################
M PROC NEAR
	CLC
	MOV AX,X
	MOV DX,0
	MOV BX,Y
	MUL BX            ; x*y --->result,result+2
 	MOV RESULT,AX
	MOV RESULT+2,DX
	MOV AX,X+2
	MOV DX,0
	MUL BX            ; (x+2)*y --->result+2,result+4
	ADD RESULT+2,AX
	ADC RESULT+4,DX
	MOV AX,X
	MOV DX,0
	MOV BX,Y+2
	MUL BX            ; x*(y+2) --->result+2,result+4
	ADD RESULT+2,AX
	ADC RESULT+4,DX
	MOV AX,X+2
	MOV DX,0
	MUL BX            ; (x+2)*(y+2) --->result+4,result+6
	ADC RESULT+4,AX
	ADC RESULT+6,DX
	LEA DX,RES       ;calculate and output
	MOV AH,09H
	INT 21H
	CALL OUTPUT1
	RET
M ENDP
;############### DIVIDED BY ############################
D PROC NEAR               ;result+4,result+6 is the quotient, result,result+2 is the remain
	MOV CX,0          ;cx reserve result+4's value
	MOV DX,0          ;dx reserve result+6's value
	CMP Y+2,0
	JNZ L10
	CMP Y,0
	JNZ L10
	LEA DX,ERR
	MOV AH,09H
	INT 21H
	RET
L10:	MOV AX,X+2        ;compare x and y
	CMP AX,Y+2        ;if x >= y 
	JNBE  L13         ;then (cx)+1 --> cx, and (dx) + carry ---> dx
	JE  L12           ;if x < y
L11:	MOV AX,X          ;then x--->result,result+2
	MOV RESULT,AX     ;and (cx),(dx) --->result+4,result+6
	MOV AX,X+2
	MOV RESULT+2,AX
	MOV RESULT+4,CX
	MOV RESULT+6,DX
	LEA DX,RES        ; output
	MOV AH,09H
	INT 21H
	CALL OUTPUT2
	RET
L12:	MOV AX,X
	CMP AX,Y
	JNB L13
	JMP L11
L13:	ADD CX,1
	ADC DX,0
	MOV AX,X
	SUB AX,Y
	MOV X,AX
	MOV AX,X+2
	SBB AX,y+2
	MOV X+2,AX
	JMP L10
	RET
D ENDP
;############## OUTPUT1(FOR ADD,SUBTRACT,MULTIPLY) ##########
OUTPUT1 PROC NEAR           ;similar to the division
	MOV DL,0            
	MOV BX,0            ;compare with 10^n,(0<= n <= 11)
	MOV SI,0         
	MOV AL,SIGN         ;if (result >= 10^n)
	CMP AL,1
	JNZ L14             ;{ (dl)+1 ---> dl
	MOV DL,'-'
	MOV AH,02H          ;  result - 10^n ---> [result]
	INT 21H
	MOV DL,0            ;  compare with 10^n again }
L14:	MOV AX,RESULT+4
	CMP AX,DCB[SI]      ;else 
	JNBE  L16
        JB  L15             ;{  (dl) ---> outstring[bx]
	MOV AX,RESULT+2
	CMP AX,DCB[SI+2]    ;   (si)+6 ---> si
	JNBE  L16
	JB  L15             ;   (bx)+1 ---> bx
	MOV AX,RESULT
	CMP AX,DCB[SI+4]    ;   compare with 10^n-1 }   
	JNB L16               
L15:	MOV OUTSTRING[BX],DL
	ADD SI,6
	MOV DL,0
	INC BX
	CMP BX,12
	JNZ L14
	JMP L17
L16: 	INC DL
	MOV AX,RESULT
	SUB AX,DCB[SI+4]
	MOV RESULT,AX
	MOV AX,RESULT+2
	SBB AX,DCB[SI+2]
	MOV RESULT+2,AX
	MOV AX,RESULT+4
	SBB AX,DCB[SI]
	MOV RESULT+4,AX
	JMP L14
L17:    MOV CX,12
	MOV SI,0
L18:	MOV DL,OUTSTRING[SI]     ;output the bcd string
	CMP DL,0
	JNE L19
	CMP FLAG,0
	JNE L19
	JMP L20
L19:	MOV FLAG,1
	ADD DL,30H
	MOV AH,02H
	INT 21H
L20:	INC SI
	LOOP L18
	CMP FLAG,0
	JNE L21
	MOV DL,'0'
	MOV AH,02H
	INT 21H	
L21:	MOV FLAG,0
	RET
OUTPUT1 ENDP
;########### OUTPUT2 (FOR DIVIDED) ######################
OUTPUT2 PROC NEAR
	MOV AX,RESULT          ;first output the quotient
	MOV BUF,AX
	MOV AX,RESULT+2
	MOV BUF+2,AX
	MOV AX,RESULT+4
	MOV RESULT,AX
	MOV AX,RESULT+6
	MOV RESULT+2,AX
	MOV RESULT+4,0
	MOV RESULT+6,0
	CALL OUTPUT1
	MOV DL,'.'             ;then output the remain
	MOV AH,02H
	INT 21H
	MOV DL,'.'
	MOV AH,02H
	INT 21H
	MOV DL,'.'
	MOV AH,02H             ;use the output1 twice
	INT 21H
	MOV AX,BUF
	MOV RESULT,AX
	MOV AX,BUF+2
	MOV RESULT+2,AX
	CALL OUTPUT1
	RET
OUTPUT2 ENDP	
;################ REPEAT? ##############################
RE PROC NEAR
	LEA DX,AGAIN
	MOV AH,09H
	INT 21H
	MOV AH,01H
	INT 21H
	CMP AL,'Y'
	JNZ L22
	MOV TAG,1
	RET
L22:	CMP AL,'y'
	JNZ L23
	MOV TAG,1
	RET
L23:	RET
RE ENDP
;########################################################
CODE ENDS
    END START