如何在Assembly中使用for循环？

Question

I was tasked to do a code that would output the equal amount of 'Text Here' depending on the user input. However, I seem to get bewildered by my cmp function.

;Get keyboard input
mov ah, 01h 
int 21h

;Save to bl for later use
mov bl, al
jmp isa

isa:
mov ah, 09h 
mov dx, offset text 
int 21h

cmp bl, bl
jne isa
je exit

What I get with this code is only one output of 'Text' no matter what number I input.

EDIT: I tried this but now my output is infinite :(

isa:
inc bl
mov ah, 09h 
mov dx, offset ulit 
int 21h


cmp bl, 30h
jne isa
je exit

Answer 1

First of all, make sure that you initialize the BX register to zero before you start your loop:

...
xor bx,bx
isa:
...

To avoid the DOS interrupt to overwrite the contents of your (used) BX register, secure it on the stack (not sure about the calling conventions of DOS interrupts, was too long ago for me):

...
push bx
int 21h
pop bx