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Friday, February 21, 2014
ASSUME
DS: DATA,
CS: CODE
DATA SEGMENT ; start of data segment
N DB 07H ; initialize the N value
R DB 05H ; R value
RESULT DB ? ; Variable to
store the result
MSG1 DB 0DH, 0AH,"NCR IS :
","$"
MSG2 DB 0DH, 0AH,"
NCR COMPUTATION IS NOT POSSIBLE (VALUE OF N< R)","$"
DATA ENDS ; end of data
segment
DISP MACRO MSG
MOV DX, OFFSET MSG ; DISP macro
definition, to display the message whose offset is in DX using
MOV AH, 09H ; 09H with DOS 21H interrupt.
INT 21H
ENDM ; end of macro definition.
CODE SEGMENT
START: MOV AX, DATA ; data segment initialization
MOV
DS, AX
MOV
AL, N ; store the N value in AL
MOV
BL, R ; store the R value in BL
CMP
AL, BL ; compare N and R value
JB STOP ; if N value is < than R value, then
jump to label STOP
MOV
RESULT, 0 ; otherwise
perform ncr computation, initialize RESULT variable to 0
CALL
FNCR ; call FNCR
procedure, to perform ncr computation.
DISP
MSG1 ; invoke the macro to display MSG1
MOV AL, RESULT ; ncr value (Hex) stored in RESULT is copied to AL.
AAM ; convert the 2 digit result in AL to unpacked BCD.
ADD AX, 3030H ; add
3030H to AX
PUSH
AX ; store in stack memory
MOV DL, AH ; display the upper digit of the result
on the screen using 02H with
MOV AH,
02H ; DOS 21H interrupt.
INT
21H
POP AX ; retrieve the original AX content from
stack
MOV DL, AL
MOV AH, 02H ; display the upper digit of the result on the screen using 02H
with
INT 21H ;DOS
21H interrupt.
JMP EXIT ; jump to label EXIT and terminate
STOP : DISP MSG2 ; invoke
the macro to display MSG2 (ncr is not possible)
EXIT : MOV AH, 4CH ; terminate the
program
INT 21H
FNCR PROC NEAR ; start of FNCR procedure
CMP AL, BL ;
compare N and R value
JE
NCR1 ;
if n = r then jump to label NCR1
to store the value 1 in RESULT variable.
CMP BL, 00 ; otherwise compare r value with 0
JE NCR1 ;
if r = 0, then jump to label NCR1
to store the value 1 in RESULT variable.
CMP BL, 01 ; otherwise compare r value with 01
JE NCRN ;
if r = 1, then jump to label NCRN
to store the ‘n’
value in RESULT variable.
DEC AL ;
decrement n by 1, so that n = n-1
CMP AL, BL ; then compare r value with n-1
JE ADD1 ;
if r = n-1, then jump to label ADD1, to
increment the ‘n’ value by 1.
; to get the n value which is already decremented by 1(n = n-1+1 = n)
PUSH AX ; push n-1 to stack
PUSH BX ; push ‘r’ to stack
CALL
FNCR ;
call FNCR procedure (recursive) to perform n-1Cr
POP BX ;
pop r
POP
AX ;
pop n-1
DEC BL ; decrement r
PUSH AX ; push
n-1
PUSH BX ;
push r-1
CALL
FNCR ;
call FNCR procedure to compute n-1C r-1
POP BX ;
pop r-1
POP AX ; pop n-1
RET ; return from
procedure
NCR1: INC RESULT ; increment result by 1
RET ; return
ADD1: INC AL ; increment n value by 1 ( since n
is decremented )
NCRN: ADD RESULT, AL ;
add result and n
RET ; return to main
program
FNCR ENDP ;end
of procedure
CODE ENDS ;
end of code segment
END START ; end of program
Output:
For
sample input N = 07H and R = 05H
D:\MASM>
Masm 8a.asm;
D:\MASM>
Link 8a.obj;
ASSUME CS: CODE, DS: DATA
DATA SEGMENT ; start of data
segment
MSG1 DB 0DH, 0AH,'ENTER YOUR NAME : ', '$'
MSG2 DB 'WHAT IS YOUR NAME? ',
'$'
STR DB
25 DUP(' '), '$' ; 25 bytes of STR array (blank) is declared to store
the user entered name.
X DB 04H ; X coordinate
value
Y DB 12H ; Y
coordinate value
DATA ENDS
DISPLAY MACRO MSG ; DISPLAY macro definition starts
MOV DX, OFFSET MSG
MOV AH, 09H ; display the message whose offset is in
DX using 09H
INT 21H ; with DOS 21H interrupt.
ENDM ; end of macro definition
CODE SEGMENT
START:
MOV AX, DATA ; data segment initialization
MOV DS, AX
DISPLAY MSG1 ; invoke the DISPLAY macro to display
MSG1
MOV SI, OFFSET STR ; SI
point to the 1st memory location of STR array
BACK: MOV AH, 01H ; read a character from keyboard using
01H service
INT 21H ; with 21h interrupt, then compare with
enter key
CMP AL, 0DH ; if yes terminate, otherwise store in
STR array pointed by SI JE
STOP ; if yes terminate,
MOV [SI], AL ; otherwise store in STR array pointed by
SI
INC
SI ; increment SI, to point to the next
location of STR array
JMP BACK ; jump to BACK to
read the next character
STOP: MOV
AH, 07H ; service number
to clear the screen
MOV AL, 00H
; Number of lines to scroll; 00 blank
screen.
MOV BH, 0FH ; attribute of
character; 0F white and 00 black
MOV CX, 00H ; CH=00 Y coordinate of upper left corner
and
; CL=00 X
coordinate of upper right corner.
MOV DH, 31H ; Number of rows;
MOV DL, 79H ; Number of columns;
INT 10H ; BIOS interrupt
to clear the screen is invoked
MOV
AH, 02H ; service number to set the cursor
MOV BH, 00H ; set video Page number to 0
MOV DH, Y ; store row
number in DH (Y coordinate)
MOV
DL, X ; store the
column number (X) in DL register
INT
10H ;
BIOS interrupt to set the cursor is invoked.
DISPLAY MSG2 ; invoke the
DISPLAY macro to display MSG2.
DISPLAY STR ; invoke the
DISPLAY macro to display STR array contents
MOV AH, 4CH ; terminate the program
INT 21H
CODE ENDS ; end of code segment
END
START ; end of program
Output:
D:\MASM>
Masm 7a.asm;
D:\MASM>
Link 7a.obj;
D:\MASM>
TD 7a.exe
Press
F7 to trace the program (line by
line execution).
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