Chapter 6: Creating SUBs and FUNCTIONs (Part I)

6.1

Introduction
It's no secret, even I didn't use SUBs or FUNCTIONs for my first couple of "projects." Admittedly, these weren't great projects, but you may want to hold off on creating SUBs or FUNCTIONs until you're more comfortable with the BASICs.

6.2

Information about SUBs
SUBs (subroutines, or often called procedures), can be thought of as a "small" module or program. Imagine first creating two games, TIC TAC TOE, and PAC-MAN. You can define two subs for this:

       SUB TicTacToe
         :
       END SUB
       
       SUB PacMan
         :
       END SUB

Now, if you wanted to play Pac-Man, you can CALL the SUB simply by doing this:

       CALL PacMan

This will execute the code found in SUB PacMan. This is just a simple example, and not very useful.

6.3

Passing variables with SUBs
When you create a subroutine, you usually want to pass some kind of information to it. Let's think about drawing a triangle on the screen in graphics mode. What kind of information do we need passed to our SUB Triangle?

 SUB Triangle(X1,Y1,X2,Y2,X3,Y3)

A triangle requires 3 (X,Y) points, so the above subroutine takes 6 arguments. It's up to you how you want to interpret the data. To be absolutely sure we only want INTEGER values, we should do this:

 SUB Triangle(X1%,Y1%,X2%,Y2%,X3%,Y3%)
   or
 SUB Triangle(X1 AS INTEGER, ...

You can have a mixture of data types as arguments, they don't all have to be INTEGERs or all STRINGs, etc. Now, just call the Triangle SUB and pass the relevent data:

  CALL Triangle(10,10,20,15,5,50)
  CALL Triangle(100,66,55,4,150,100)

The Triangle SUB is reuseable, so you can see how useful SUBs are. I'll let you complete the SUB Triangle as an exercise.

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Next: Chapter 7