Guessing Game in Assembly
This assembly language program is designed to create a very simple game where user is allowed to guess a hard coded number between 1 and 255. This hard coded number can be replaced by a randomly generated number using a “random number generator” for EMU8086, which is bit complex because EMU8086 do not contain an instruction to do this implicitly. Program will output if guess is higher or lower than the input number. The code is well commented so that it can be used by anyone who is interested in learning assembly language.
Assembler
This code is written for EMU8086
http://www.emu8086.com/
Flow of the Program
System will print a message saying “Please enter a valid number:” Enter a number and *** Press ENTER *** key to continue.
The approach used to code this program made validating so easy. Because of that such features are implemented in this program. This system do NOT require user to enter a three degit numbers.
Ex : Inputs like 32,1 are valid. They will be converted to nemeric representation.
34 = 034 (Implicitly)
1 = 001 (Implicitly)
Also is users enter a value out of rage such as -1, 256,….. system will print:
“Error – Number out of range!”
Finally, it asks if user wants to retry, when a correct guess is made.
DEMO RUN
*** means ‘Enter key’ is pressed ****
Please enter a valid number: 0
Value is MorePlease enter a valid number: 128
Value is MorePlease enter a valid number: 170
Value if LessPlease enter a valid number: 255
Value if LessPlease enter a valid number: 256
Error – Number out of range!Please enter a valid number: -1
Error – Number out of range!Please enter a valid number: 3333
Error – Number out of range!Please enter a valid number: 169
You have made fine Guess!Retry [y/n] ?
Source Code
; E091040066_A1.asm:
; Author: Ayoma Gayan Wijethunga
; Date : 03/05/2011
; ****** This code is written for EMU8086 *****
.model small
.stack 100h
.data
number db 169d ;variable 'number' stores the random value
;declarations used to add LineBreak to strings
CR equ 13d
LF equ 10d
;String messages used through the application
prompt db CR, LF,'Please enter a valid number : $'
lessMsg db CR, LF,'Value if Less ','$'
moreMsg db CR, LF,'Value is More ', '$'
equalMsg db CR, LF,'You have made fine Guess!', '$'
overflowMsg db CR, LF,'Error - Number out of range!', '$'
retry db CR, LF,'Retry [y/n] ? ' ,'$'
guess db 0d ;variable user to store value user entered
errorChk db 0d ;variable user to check if entered value is in range
param label Byte
.code
start:
; --- BEGIN resting all registers and variables to 0h
MOV ax, 0h
MOV bx, 0h
MOV cx, 0h
MOV dx, 0h
MOV BX, OFFSET guess ; get address of 'guess' variable in BX.
MOV BYTE PTR [BX], 0d ; set 'guess' to 0 (decimal)
MOV BX, OFFSET errorChk ; get address of 'errorChk' variable in BX.
MOV BYTE PTR [BX], 0d ; set 'errorChk' to 0 (decimal)
; --- END resting
MOV ax, @data ; get address of data to AX
MOV ds, ax ; set 'data segment' to value of AX which is 'address of data'
MOV dx, offset prompt ; load address of 'prompt' message to DX
MOV ah, 9h ; Write string to STDOUT (for DOS interrupt)
INT 21h ; DOS INT 21h (DOS interrupt)
MOV cl, 0h ; set CL to 0 (Counter)
MOV dx, 0h ; set DX to 0 (Data register used to store user input)
; -- BEGIN reading user input
while:
CMP cl, 5d ; compare CL with 10d (5 is the maximum number of digits allowed)
JG endwhile ; IF CL > 5 then JUMP to 'endwhile' label
MOV ah, 1h ; Read character from STDIN into AL (for DOS interrupt)
INT 21h ; DOS INT 21h (DOS interrupt)
CMP al, 0Dh ; compare read value with 0Dh which is ASCII code for ENTER key
JE endwhile ; IF AL = 0Dh, Enter key pressed, JUMP to 'endwhile'
SUB al, 30h ; Substract 30h from input ASCII value to get actual number. (Because ASCII 30h = number '0')
MOV dl, al ; Move input value to DL
PUSH dx ; Push DL into stack, to get it read to read next input
INC cl ; Increment CL (Counter)
JMP while ; JUMP back to label 'while' if reached
endwhile:
; -- END reading user input
DEC cl ; decrement CL by one to reduce increament made in last iteration
CMP cl, 02h ; compare CL with 02, because only 3 numbers can be accepted as IN RANGE
JG overflow ; IF CL (number of input characters) is greater than 3 JUMP to 'overflow' label
MOV BX, OFFSET errorChk ; get address of 'errorChk' variable in BX.
MOV BYTE PTR [BX], cl ; set 'errorChk' to value of CL
MOV cl, 0h ; set CL to 0, because counter is used in next section again
; -- BEGIN processing user input
; -- Create actual NUMERIC representation of
;-- number read from user as three characters
while2:
CMP cl,errorChk
JG endwhile2
POP dx ; POP DX value stored in stack, (from least-significant-digit to most-significant-digit)
MOV ch, 0h ; clear CH which is used in inner loop as counter
MOV al, 1d ; initially set AL to 1 (decimal)
MOV dh, 10d ; set DH to 10 (decimal)
; -- BEGIN loop to create power of 10 for related possition of digit
; -- IF CL is 2
; -- 1st loop will produce 10^0
; -- 2nd loop will produce 10^1
; -- 3rd loop will produce 10^2
while3:
CMP ch, cl ; compare CH with CL
JGE endwhile3 ; IF CH >= CL, JUMP to 'endwhile3
MUL dh ; AX = AL * DH whis is = to (AL * 10)
INC ch ; increment CH
JMP while3
endwhile3:
; -- END power calculation loop
; now AL contains 10^0, 10^1 or 10^2 depending on the value of CL
MUL dl ; AX = AL * DL, which is actual positional value of number
JO overflow ; If there is an overflow JUMP to 'overflow'label (for values above 300)
MOV dl, al ; move restlt of multiplication to DL
ADD dl, guess ; add result (actual positional value of number) to value in 'guess' variable
JC overflow ; If there is an overflow JUMP to 'overflow'label (for values above 255 to 300)
MOV BX, OFFSET guess ; get address of 'guess' variable in BX.
MOV BYTE PTR [BX], dl ; set 'errorChk' to value of DL
INC cl ; increment CL counter
JMP while2 ; JUMP back to label 'while2'
endwhile2:
; -- END processing user input
MOV ax, @data ; get address of data to AX
MOV ds, ax ; set 'data segment' to value of AX which is 'address of data'
MOV dl, number ; load original 'number' to DL
MOV dh, guess ; load guessed 'number' to DH
CMP dh, dl ; compare DH and DL (DH - DL)
JC greater ; if DH (GUESS) > DL (NUMBER) cmparision will cause a Carry. Becaus of that if carry has been occured print that 'number is more'
JE equal ; IF DH (GUESS) = DL (NUMBER) print that guess is correct
JG lower ; IF DH (GUESS) < DL (NUMBER) print that number is less
equal:
MOV dx, offset equalMsg ; load address of 'equalMsg' message to DX
MOV ah, 9h ; Write string to STDOUT (for DOS interrupt)
INT 21h ; DOS INT 21h (DOS interrupt)
JMP exit ; JUMP to end of the program
greater:
MOV dx, offset moreMsg ; load address of 'moreMsg' message to DX
MOV ah, 9h ; Write string to STDOUT (for DOS interrupt)
INT 21h ; DOS INT 21h (DOS interrupt)
JMP start ; JUMP to beginning of the program
lower:
MOV dx, offset lessMsg ; load address of 'lessMsg' message to DX
MOV ah, 9h ; Write string to STDOUT (for DOS interrupt)
INT 21h ; DOS INT 21h (DOS interrupt)
JMP start ; JUMP to beginning of the program
overflow:
MOV dx, offset overflowMsg ; load address of 'overflowMsg' message to DX
MOV ah, 9h ; Write string to STDOUT (for DOS interrupt)
INT 21h ; DOS INT 21h (DOS interrupt)
JMP start ; JUMP to beginning of the program
exit:
; -- Ask user if he needs to try again if guess was successful
retry_while:
MOV dx, offset retry ; load address of 'prompt' message to DX
MOV ah, 9h ; Write string to STDOUT (for DOS interrupt)
INT 21h ; DOS INT 21h (DOS interrupt)
MOV ah, 1h ; Read character from STDIN into AL (for DOS interrupt)
INT 21h ; DOS INT 21h (DOS interrupt)
CMP al, 6Eh ; check if input is 'n'
JE return_to_DOS ; call 'return_to_DOS' label is input is 'n'
CMP al, 79h ; check if input is 'y'
JE restart ; call 'restart' label is input is 'y' ..
; "JE start" is not used because it is translated as NOP by emu8086
JMP retry_while ; if input is neither 'y' nor 'n' re-ask the same question
retry_endwhile:
restart:
JMP start ; JUMP to begining of program
return_to_DOS:
MOV ax, 4c00h ; Return to ms-dos
INT 21h ; DOS INT 21h (DOS interrupt)
end start
RET
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