# Program that will read a positive binary number and print its factorial in decimal form using MUL and DIV instructionsand use OUTDEC procedure........

``` .MODEL SMALL
.STACK 100H

.DATA
PROMPT_1  DB  \'Enter a Positive Binary number ( max. 8-bit ) : \$\'
PROMPT_2  DB  0DH,0AH,\'The Factorial of the given number in Decimal form is : \$\'
ILLEGAL   DB  0DH,0AH,\'Illegal character. Try again : \$\'

.CODE
MAIN PROC
MOV AX, @DATA                ; initialize DS
MOV DS, AX

LEA DX, PROMPT_1             ; load and display the string PROMPT_1
MOV AH, 9
INT 21H

CALL BINARY_INPUT            ; call the procedure BINARY_INPUT

CALL FACTORIAL               ; call the procedure FACTORIAL

LEA DX, PROMPT_2             ; load and display the string PROMPT_2
MOV AH, 9
INT 21H

MOV AX, BX                   ; set AX=BX

CALL OUTDEC                  ; call the procedure OUTDEC

MOV AH, 4CH                  ; return control to DOS
INT 21H
MAIN ENDP

;-------------------------  Procedure Definitions  ------------------------;

;----------------------------  BINARY_INPUT  ------------------------------;

BINARY_INPUT PROC
; this procedure will read a number in binary form
; input : none
; output : store binary number in BL
; uses : MAIN

JMP @BEGIN                     ; jump to label @BEGIN

@ERROR:                        ; jump label

LEA DX, ILLEGAL                ; load and display the string ILLEGAL
MOV AH, 9
INT 21H

@BEGIN:                        ; jump label

MOV CX, 8                      ; initialize loop counter
XOR BX, BX                     ; clear BX
MOV AH, 1                      ; set input function

@INPUT:                        ; loop label
INT 21H                      ; read a digit

CMP AL, 0DH                  ; compare input and CR
JE @END                      ; jump to label @END if input is CR

CMP AL, 30H                  ; compare AL with 0
JL @ERROR                    ; jump to label @ERROR if AL<0

CMP AL, 31H                  ; compare AL with 1
JG @ERROR                    ; jump to label @ERROR if AL>1

AND AL, 0FH                  ; convert ascii to decimal code
SHL BL, 1                    ; shift BL by 1 position towards left
OR  BL, AL                   ; place the input decimal digit in BL
LOOP @INPUT                    ; jump to label @INPUT if CX!=0

@END:                          ; jump label

RET                            ; return control to the calling procedure
BINARY_INPUT ENDP

;-------------------------------  OUTDEC  ---------------------------------;

OUTDEC PROC
; this procedure will display a decimal number
; input : AX
; output : none
; uses : MAIN

PUSH BX                        ; push BX onto the STACK
PUSH CX                        ; push CX onto the STACK
PUSH DX                        ; push DX onto the STACK

XOR CX, CX                     ; clear CX
MOV BX, 10                     ; set BX=10

@OUTPUT:                       ; loop label
XOR DX, DX                   ; clear DX
DIV BX                       ; divide AX by BX
PUSH DX                      ; push DX onto the STACK
INC CX                       ; increment CX
OR AX, AX                    ; take OR of Ax with AX
JNE @OUTPUT                    ; jump to label @OUTPUT if ZF=0

MOV AH, 2                      ; set output function

@DISPLAY:                      ; loop label
POP DX                       ; pop a value from STACK to DX
OR DL, 30H                   ; convert decimal to ascii code
INT 21H                      ; print a character
LOOP @DISPLAY                  ; jump to label @DISPLAY if CX!=0

POP DX                         ; pop a value from STACK into DX
POP CX                         ; pop a value from STACK into CX
POP BX                         ; pop a value from STACK into BX

RET                            ; return control to the calling procedure
OUTDEC ENDP

;-----------------------------  FACTORIAL  --------------------------------;

FACTORIAL PROC
; this procedure will computes the factorial of a given number
; input : BL
; output : store the factorial of the number in BX
; uses : MAIN

MOV AX, 1                      ; set AX=1

XOR CX, CX                     ; clear CX
MOV CX, BX                     ; set CX=BX

@LOOP:                         ; loop label
MUL CX                       ; multiply CX with AL i.e. AX=AL*CX
LOOP @LOOP                     ; jump to label @LOOP if CX!=0

MOV BX, AX                     ; set BX=AX

RET                            ; return control to the calling procedure
FACTORIAL ENDP

END MAIN
```