Fairly simple assembly program

[orgcaptainnemo]

Alright,

I'm writing a little assembly program that takes someone's score (0-100) and then tells you what letter grade they will get. So, 90-100 = A, 80-89 = B, and so on.

I'm writing it in NASM on the 8086, and right now I can get it to read my input correctly. Its stored in:

buf:
max     db      4
count   db      0
input   db      0,0,0,0

Now I need to find a way to compare what they've inputted into 'input' with 90, 80, etc... I know how to use the cmp and jmp commands (ja, jna, jb, jnb, etc...) BUT I'm not sure how to create a piece of data that I can directly compare with my input.

Since the input is a string in ASCII and the jmp commands are looking at the hex value. So simply saying:

mov bx, input
mov ax, ninety ; assume ninety was declared as '90'
cmp bx, ax 
jb else              ; if bx is lower than 90 than go to the else

mov ah, 9
mov dx, msga ; msg says the user gets an A
int 0x21

else: <IMAGINE MORE CODE>

If I could just get some suggestions or ideas on how to compare this it would be really great.

Thanks

 

[Josh_B]

Sorry to hijack your thread, but are you taking a course, or are you learning from a book? (I'm looking for a good assembly book... they're hard to find, I've found.)

 

[orgcaptainnemo]

Its a class taught by an idiot, and this idiot told us not to buy the book. Which I regret now.

BUY THE BOOK NO MATTER WHAT.

 

[[MS]]

You can only compare a number with a number...

Given that and you're given the offset to some defined bytes that contain a string; the string should probably be converted to a number.

Using whatever info you're teacher has given, or even just google, you'll probably be able to figure out how to turn and ASCII string into a number.

Then what you'd have is two numbers, and you already know cmp works.

Additionally, you may want to think about an alternate implementation. It might be able to be done with less code than you think...