Why does int 16h in my assembly language program cause a crash?

I'm trying to learn Assembly language, and I'm trying to do one of the examples in the book.

It compiles fine, but when ever I try to run my program it crashes. When I debug the program it says

'Unhandled exception in temp.exe;0xC0000005;Access Violation' and tells me that the line

int 16h

is what is causing the crash. The book tells me specifially to use this command, so I can't change it to something else. So does anyone know what I can do?

I'm using Windows XP with SP3. I've got an Intel Celeron processor.

Here's my code:

mov bx, 0

cmp bx, 80

jz done1

mov ah, 0

int 16h

mov myvar[2], al

inc bx

cmp al, 0dh

jz done2

done1: mov myvar, 0dh

done2: mov bx, 0

myloop: cmp myvar[bx], 0dh

jz done3

mov ah, 03

mov al, myvar[bx]

int 10h

inc bx

;jmp myloop

done3: exit