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Newcomers DBPro Corner / [Tutorial] Functions, subroutines, and where we can use them

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calcyman
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Location: The Uncertainty Principle
Posted: 26th Oct 2007 14:02
Functions are best for elements that aren't specific to a single game. Drawing a filled-in circle would be best as a function (I've actually made that function for you) Subroutines should be used when you have chunks of code that you want to clear up.

To call a subroutine, use gosub label (where label is the title of the subroutine)

An example of a subroutine is here:



The subroutine is to make a waterwheel turn in a Lemmings game.

Let's analyse the main segments:



That tells us that it is the start of the subroutine.



That tells us to jump back into the main loop after being called.

For example, an FPS loop might have about 1200 lines of code, but it can be simplified to:



followed by a long list of subroutines.

You may learn how to make functions, but remember this:

A FUNCTION CAN ONLY READ THE VARIABLES YOU PASS TO IT.

If you don't pass a variable to it, it will not recognise it, and will see it as being a value of 0.

Try looking at my functions (in my #include tutorial) to help you understand the concept.

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Jeff032
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Posted: 26th Oct 2007 14:14
Quote: "A FUNCTION CAN ONLY READ THE VARIABLES YOU PASS TO IT."


They can read global variables...

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SimSmall
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Location: United Kingdom
Posted: 26th Oct 2007 14:35
Quote: "They can read global variables..."


And arrays dimensionised outside the function.
calcyman
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Posted: 26th Oct 2007 15:39
I didn't make this tutorial to attract criticism, and most newcomers won't use globals prior to learning functions. And it's bad practice to make a function that relies on globals, as it isn't very flexible (it can't easily be ported between source code)

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Zotoaster
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Location: Scotland
Posted: 26th Oct 2007 17:24
You havent mentioned returning variables, local variables, issues with functions (i.e. not being able to pass arrays, being able to pass UDT vars but not return them, etc), you havent compared functions to subroutines, speed-wise, or functionality-wise, and above that, you havent even shown us any code for functions.

Sorry for the critisism, but it's really needed. I think there's already a tut on functions anyway, but I'm not sure.

"It's like floating a boat on a liquid that I don't know, but I'm quite happy to drink it if I'm thirsty enough" - Me being a good programmer but sucking at computers
Jeff032
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Posted: 26th Oct 2007 18:25
Quote: "Quote: "And arrays dimensionised outside the function. "

And arrays dimensionised inside a function (same or other) if the GLOBAL keyword has been used."


Actually, you can access an array from anywhere in the code no matter where you dim it without using global. Unless you use the local keyword when dimensioning an array, it is automatically global.

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Jeff032
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Posted: 26th Oct 2007 19:26
Strange, I had tested it and it worked fine. I'm using 6.6b.

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