.model small
org 100h
.data
msg1 db "Enter a letter: $"
word db "BABA$"
word_length db 4 ; length of word
input1 db 10,?,10 dup('$') ; buffer for input
letter_pos db 0 ; counter for letter position
.code
main proc
mov ah, 09h
lea dx, msg1
int 21h
mov ah, 0ah
lea dx, input1
int 21h
mov ah, 02h ; setting initial cursor position
mov dh, 1
mov dl, 0
int 10h
; main code
lea si, input1[2]
lea di, word
mov cl, word_length
compare:
cmp cl, 0
je exit
mov bl, [si]
mov bh, [di]
cmp bl, bh
je correct_letter
inc letter_pos
inc di
dec cl
jmp compare
correct_letter:
; set cursor position
mov ah, 02h
mov dh, 1
mov dl, letter_pos
int 10h
mov ah, 09h
lea dx, input1+2
int 21h
inc letter_pos
mov al, letter_pos
dec cl
jmp compare
exit:
MOV ah, 4ch
int 21h
main endp
end main
I can't seem to work out why this doesn't work. I've set it so that every iteration of the loop, the letter_pos is incremented, meaning it will go the next column, or in this case to the next position of the word. Am I missing something here?
I'm very new to assembly language so pardon my mess of a code, I'm trying to learn this for a school project. Your help will be appreciated!
I'm expecting it to be like this:
Enter a letter: A
A A
or
Enter a letter: B
B B
I tried some ways in an attempt to fix this, including changing 0rg 100g to .stack 100h (idk too much how this matters tho) and some other things, i'm still new so idk yet how to fully debug this.
Don't use org 100h when specifying any model other than .model tiny.
The mention of org 100h means that you create a DOS executable file bearing the .COM extension. That's an excellent type of executable for anyone that is still new to assembly. The crucial benefit is that you don't need to worry about setting up the segment registers since at startup CS=DS=ES=SS, and that you can forget about .model, .data, .code, main proc, main endp, and end main.
inc letter_pos mov al, letter_pos
Here is why your program would hang if the loop weren't limited to just 4 iterations. This mov al, letter_pos needs to become inc di. Currently the program keeps re-testing the same matching character again and again.
mov ah, 09h lea dx, input1+2 int 21h
And this is another peculiarity. Because you have used the DOS.BufferedInput funtion 0Ah for inputting that single character "A", the memory at input1+2 actually contains next 3 bytes: 65, 13, 36. So you will display the character "A" but the blinking cursor will return to the left side of the screen. That's one reason to get confused!
org 100h ; Create .COM program
xor dx, dx ; Row DH=0, Column DL=0
mov ah, 02h ; setting initial cursor position
int 10h ; BIOS.SetCursorPosition
mov dx, OFFSET msg
mov ah, 09h ; DOS.PrintString
int 21h
mov ah, 01h ; DOS.KeyboardInputWithEcho
int 21h ; -> AL
mov bl, al ; Move to a safe place (certainly not AL, AH, DL, DH)
mov di, OFFSET txt
mov cl, txt_length ; 1+
compare:
cmp bl, [di]
jne incorrect_letter
correct_letter:
mov dh, 1
mov dl, letter_pos
mov ah, 02h
int 10h ; BIOS.SetCursorPosition
mov dl, bl
mov ah, 02h ; DOS.DisplayOutput
int 21h ; -> AL
incorrect_letter:
inc letter_pos
inc di
dec cl
jnz compare
exit:
mov ax, 4C00h ; DOS.TerminateWithReturncode
int 21h
; --------------------
; The data comes below the code
; --------------------
msg db "Enter a letter: $"
txt db "BABA"
txt_length db 4 ; length of word
letter_pos db 0 ; counter for letter position
I'm trying to learn this for a school project. Your help will be appreciated!
The code that I present to you probably contains a lot of new stuff. If you're serious about 'learning this' then don't just copy-paste but look closely and keep asking yourself "Why did he choose to write it that way? Happy learning!