Day 5

Subroutines

	Subroutines, almost just like C or BASIC...

Labels
	We've seen labels before when we saw variables, except these labels that mark a location in
code have a color (':') after them, such as:

	outputA:
		mov ah,2
		mov dl,'A'
		int 21h

These labels can be accessed like variables also, and that's how self-modifying code works.

The CALL and RET Instructions
	The CALL instruction calls a function specified by a label and a RET instruction returns
to the main program, such as the following:

	mov dl,'G'
	call outputLetter
	mov dl,'o'
	call outputLetter
	call ExitProgram
outputLetter:
	mov ah,2
	int 21h
	ret  ; returns to instruction after the CALL
ExitProgram:
	mov ah,4ch
	int 21h    ; note that since the program will exit, there's no need for a RET.

The above program will output Go in DOS.

This Day In Review

	With what you know now, you can write a program to output the alphabet.
It'll be (very) long, but you can do it!

	Tomorrow, Functions in assembly!

	Happy coding!,
		-Mike H


Intro - Day 6