.MODEL SMALL
.STACK 100H
.DATA
PROMPT_1 DB 'Enter a Positive Decimal number : $'
PROMPT_2 DB 0DH,0AH,'The Factorial of the given number in Decimal form is : $'
.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 INDEC ; call the procedure INDEC
CALL FACTORIAL ; call the procedure FACTORIAL
PUSH AX ; push AX onto the STACK
LEA DX, PROMPT_2 ; load and display the string PROMPT_2
MOV AH, 9
INT 21H
POP AX ; pop a value from STACK into AX
CALL OUTDEC ; call the procedure OUTDEC
MOV AH, 4CH ; return control to DOS
INT 21H
MAIN ENDP
;**************************************************************************;
;**************************************************************************;
;------------------------- Procedure Definitions ------------------------;
;**************************************************************************;
;**************************************************************************;
;**************************************************************************;
;------------------------------- INDEC ----------------------------------;
;**************************************************************************;
INDEC PROC
; this procedure will read a number indecimal form
; input : none
; output : store binary number in AX
; uses : MAIN
PUSH BX ; push BX onto the STACK
PUSH CX ; push CX onto the STACK
PUSH DX ; push DX onto the STACK
JMP @READ ; jump to label @READ
@SKIP_BACKSPACE: ; jump label
MOV AH, 2 ; set output function
MOV DL, 20H ; set DL=' '
INT 21H ; print a character
@READ: ; jump label
XOR BX, BX ; clear BX
XOR CX, CX ; clear CX
XOR DX, DX ; clear DX
MOV AH, 1 ; set input function
INT 21H ; read a character
CMP AL, "-" ; compare AL with "-"
JE @MINUS ; jump to label @MINUS if AL="-"
CMP AL, "+" ; compare AL with "+"
JE @PLUS ; jump to label @PLUS if AL="+"
JMP @SKIP_INPUT ; jump to label @SKIP_INPUT
@MINUS: ; jump label
MOV CH, 1 ; set CH=1
INC CL ; set CL=CL+1
JMP @INPUT ; jump to label @INPUT
@PLUS: ; jump label
MOV CH, 2 ; set CH=2
INC CL ; set CL=CL+1
@INPUT: ; jump label
MOV AH, 1 ; set input function
INT 21H ; read a character
@SKIP_INPUT: ; jump label
CMP AL, 0DH ; compare AL with CR
JE @END_INPUT ; jump to label @END_INPUT
CMP AL, 8H ; compare AL with 8H
JNE @NOT_BACKSPACE ; jump to label @NOT_BACKSPACE if AL!=8
CMP CH, 0 ; compare CH with 0
JNE @CHECK_REMOVE_MINUS ; jump to label @CHECK_REMOVE_MINUS if CH!=0
CMP CL, 0 ; compare CL with 0
JE @SKIP_BACKSPACE ; jump to label @SKIP_BACKSPACE if CL=0
JMP @MOVE_BACK ; jump to label @MOVE_BACK
@CHECK_REMOVE_MINUS: ; jump label
CMP CH, 1 ; compare CH with 1
JNE @CHECK_REMOVE_PLUS ; jump to label @CHECK_REMOVE_PLUS if CH!=1
CMP CL, 1 ; compare CL with 1
JE @REMOVE_PLUS_MINUS ; jump to label @REMOVE_PLUS_MINUS if CL=1
@CHECK_REMOVE_PLUS: ; jump label
CMP CL, 1 ; compare CL with 1
JE @REMOVE_PLUS_MINUS ; jump to label @REMOVE_PLUS_MINUS if CL=1
JMP @MOVE_BACK ; jump to label @MOVE_BACK
@REMOVE_PLUS_MINUS: ; jump label
MOV AH, 2 ; set output function
MOV DL, 20H ; set DL=' '
INT 21H ; print a character
MOV DL, 8H ; set DL=8H
INT 21H ; print a character
JMP @READ ; jump to label @READ
@MOVE_BACK: ; jump label
MOV AX, BX ; set AX=BX
MOV BX, 10 ; set BX=10
DIV BX ; set AX=AX/BX
MOV BX, AX ; set BX=AX
MOV AH, 2 ; set output function
MOV DL, 20H ; set DL=' '
INT 21H ; print a character
MOV DL, 8H ; set DL=8H
INT 21H ; print a character
XOR DX, DX ; clear DX
DEC CL ; set CL=CL-1
JMP @INPUT ; jump to label @INPUT
@NOT_BACKSPACE: ; jump label
INC CL ; set CL=CL+1
CMP AL, 30H ; compare AL with 0
JL @ERROR ; jump to label @ERROR if AL<0
CMP AL, 39H ; compare AL with 9
JG @ERROR ; jump to label @ERROR if AL>9
AND AX, 000FH ; convert ascii to decimal code
PUSH AX ; push AX onto the STACK
MOV AX, 10 ; set AX=10
MUL BX ; set AX=AX*BX
MOV BX, AX ; set BX=AX
POP AX ; pop a value from STACK into AX
ADD BX, AX ; set BX=AX+BX
JMP @INPUT ; jump to label @INPUT
@ERROR: ; jump label
MOV AH, 2 ; set output function
MOV DL, 7H ; set DL=7H
INT 21H ; print a character
XOR CH, CH ; clear CH
@CLEAR: ; jump label
MOV DL, 8H ; set DL=8H
INT 21H ; print a character
MOV DL, 20H ; set DL=' '
INT 21H ; print a character
MOV DL, 8H ; set DL=8H
INT 21H ; print a character
LOOP @CLEAR ; jump to label @CLEAR if CX!=0
JMP @READ ; jump to label @READ
@END_INPUT: ; jump label
CMP CH, 1 ; compare CH with 1
JNE @EXIT ; jump to label @EXIT if CH!=1
NEG BX ; negate BX
@EXIT: ; jump label
MOV AX, BX ; set AX=BX
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
INDEC 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 : AX
; output : store the factorial of the number in AX
; uses : MAIN
MOV CX, AX
MOV AX, 1 ; set AX=1
@LOOP: ; loop label
MUL CX ; multiply CX with AL i.e. AX=AL*CX
LOOP @LOOP ; jump to label @LOOP if CX!=0
RET ; return control to the calling procedure
FACTORIAL ENDP
;**************************************************************************;
;--------------------------------------------------------------------------;
;**************************************************************************;
END MAIN
;**************************************************************************;
;**************************************************************************;
;------------------------------ THE END ---------------------------------;
;**************************************************************************;
;**************************************************************************;