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Newcomers DBPro Corner / A Tutorial On Functions

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Sixty Squares
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Posted: 24th Aug 2006 23:01 Edited at: 5th Jul 2007 03:52
If you have anything that you think that I need to add, please say so. Feel free to ask questions if you don't understand something. I will do my best to answer you. Oh, and when you see things in bold, they are not full examples, but small snippets to help you understand what I am talking about.

If you cannot seem to figure out what a function is, then read this.


What is a function? How do I use one?



Functions are pretty easy to understand once you get the hang of them. What they do is allow you to create "shortcuts" or "custom commands" in your program. They can help you to accomplish many things, for they are very flexible. You can also put different values into functions. For example, if you wanted to make a tall red ghosted box, you could write:
Make object box 1,10,50,10
color object 1,rgb(255,0,0)
ghost object on 1


Or, you could make a function that would do it, like this:

Function MakeTallRedBox(OBJECT)
Make Object Box OBJECT,10,50,10
Color Object OBJECT,rgb(255,0,0)
ghost object on OBJECT
endfunction


And to use or "call" that function, just write:


MakeTallRedBox(1)


And then you will see a tall red box with the object number 1.

To make or "declare" a function, all you need to do is to write FUNCTION, and then right after that, you can write the name of your function or custom command. Note that the name can have no spaces and it cannot have the same name of a normal command. For example, you can't name your function "SYNC", becasue there is already a command named SYNC built into DarkBasic. However, when you write FUNCTION, you need to make a space between the word FUNCTION and the name of the function, that way it can tell the actual command FUNCTION and the name of your function apart. Why do functions need names? Well, if they didn't have names, then how would you call them? The name of our function above is MakeTallRedBox. What's the name of this function (open the snippet for the answer):


Function DarkBasicIsTheBest(OBJECT)
Make Object Cube OBJECT,10
endfunction




Inbetween FUNCTION and ENDFUNCTION is where you write what the function actually does. You use ENDFUNCTION to say that the function is over. So, this function:


Function CreateCube(OBJECT)
Make Object Cube OBJECT,10
endfunction


would create a cube using the object number specified in the variable OBJECT. You'll learn about that variable OBJECT on the next line

You may be wondering what the () and the word OBJECT are doing there. well, it's those () and what's in them that makes functions so special.
You can place a variable in those (), and so whatever you put in there when you call the function will be placed in that variable for the function to use. Going back to our Tall red cube example. You may have noticed that I put a 1 in the () when I called the function. Well, when I made the function, the variable called OBJECT was in those (). In this case, when the function refers to the variable OBJECT, it is refering to the number 1, because when I called the function I replaced the word OBJECT with the number 1. When I said:

Make object box OBJECT,10,50,10

in the function, I was really saying

Make Object box 1,10,50,10

because I had put a number 1 in the () when I called the function. If I had put a 2 in those () when I called the function, the function would really be saying this:

Make Object box 2,10,50,10

instead of

Make Object box OBJECT,10,50,10

because I had put a 2 in the variable OBJECT, the variable OBJECT now represents the number 2.

So basically, in order to place a value inside a variable for a function, you must put a value in the variable's place when you call the function.

Of couse, you could have a function that needs no input at all, like this one:

Function SetupGame()
sync on
sync rate 60
autocam off
endfunction


And you'd call that like this:

SetupGame()

Because you don't need to pass anything into the function, you can just leave the () blank.



Returning Values

Did you know that functions can return values? Well, they can! Creating functions that return values can be very useful, especially when trying to deal with long maths. For example, if you wanted ot find out what a number times 5 minus 3 plus 9 plus half of our original number minus 1/4 of the original number was, you could write:

N=5 `where N is our number
N=N*5-3+9+(N/2)-(N/4)


That's fine. But, what if you wanted to do it for 4 different numbers that were not in order? Say those numbers were 2 5 8 and 10. You could write:


N=2
Answer=N*5-3+9+(N/2)-(N/4)

N=5
Answer=N*5-3+9+(N/2)-(N/4)

N=8
Answer=N*5-3+9+(N/2)-(N/4)

N=10
Answer=N*5-3+9+(N/2)-(N/4)


but that's long and annoying! So, why not make a function for it:


Function DoComplexMath(N)
Answer#=N*5-3+9+(N/2)-(N/4)
endfunction Answer#


Notice the "Answer#" after endfunction. That is the value or variable that you want to return. If I don't want to return anything, I would just leave that blank, like all of the prior examples. So, if I wrote


HeyThisIsTheAnswer#=DoComplexMath(5)


then the answer to the math problem that was done in the function would be put inside the variable called "HeyThisIsTheAnswer#". Understood? And you don't need to return integer variables, nor do you need to pass them in. You can pass and return ANY kind of variable that you want. That "DoComplexMath" function returns a REAL number or a FLOAT (notice the "#" sign after the variable name "Answer"). This function is faster to use because instead of doing this:


N=2
Answer=N*5-3+9+(N/2)-(N/4)

N=5
Answer=N*5-3+9+(N/2)-(N/4)

N=8
Answer=N*5-3+9+(N/2)-(N/4)

N=10
Answer=N*5-3+9+(N/2)-(N/4)


You can just do this:


Result#=DoComplexMath(2)
Result#=DoComplexMath(5)
Result#=DoComplexMath(8)
Result#=DoComplexMath(10)


It's much cleaner.


And keep in mind that functions can only return one value, not 2, not 3, not 4. Just 1. If you want to return more values, you may want to look into GLOBAL variables (DBPro) or ARRAYS (DBC and DBPRo). But you CAN pass multiple values into functions.



Passing Multiple Values Into Functions

In our MakeTallRedBox function, we had only one value going into the function. Let's change that so that we have to specify two values: The Object number and the height of our tall red box. This is our old function:


Function MakeTallRedBox(OBJECT)
Make Object Box OBJECT,10,50,10
Color Object OBJECT,rgb(255,0,0)
ghost object on OBJECT
endfunction


That creates a tall red box with a height of 50. Let's change that. To insert multiple values into a function, all you need to do is add another variable in the part where you make the function. You separate these variables using commas (,). So, if we wanted to store the height in a variable called HEIGHT, and the object number in one called OBJECT, we would write this at the start:


Function MakeTallRedBox(OBJECT , HEIGHT)


There. Now we need to specify 2 values for our function to work: The Object number and the height. Here is the rest of our function:


Function MakeTallRedBox(OBJECT , HEIGHT)
Make Object Box OBJECT,10,HEIGHT,10
Color Object OBJECT,rgb(255,0,0)
ghost object on OBJECT
endfunction


Now, we can specify the height of our box. So, if I called the function like this:


MakeTallRedBox(1,65)


If would make a tall red box with a height of 65. Please note that when calling functions that have multiple input values (or whatever you want to call them) you must put them in the same order as you did when you declared the function. When we declared our MakeRedBox function, we had said:


MakeTallRedBox(OBJECT , HEIGHT)


with the object number first, and the height second. So, if we called the function like this:


MakeTallRedBox(65,1)


Then what would that do? Take a guess. The answer is in that code box. Open it after you've guessed.



And there you have it. Functions can accept as many input values or "parameters" as you like! You could give it 5 values, like this if you wanted!


Function AddAllTheNumbers(One,Two,Three,Four,Five)
Answer=One+Two+Three+Four+Five
endfunction Answer


That function would add up all of the numbers that you specify!

However, there is a limit to the amount of parameters that you can specify. The limit is 255. But who wants to keep track of 255 parameters anyway!? You probably couldn't even fit that many on 1 line, so this shouldn't concern you



USEFUL FUNCTION INFO

Just so you know, unless a variable was declared global earlier in the program, all variables that are used within functions are considered "Local" variables. This means that if you gave a variable called "PotsAndPans" a value of 50 outside of a function, and then in a function you used the same variable and gave it a value of 10, it would only be equal to 10 within the function. It would still be 50 outside of it. Furthermore, a variable used inside a function will not save its value for the next time that it is called. Meaning that, if you said

PotsAndPans=PotsAndPans+10

within a function, the variable would go to 10, of course, but as soon as the function ended it would go back to 0. So, the next time that function was called, it would just boost the value back up to 10, not to 20 because tha variable's value was not saved. But you can pass arrays and global variables through functions. however, if you modify them outside of a function, then they will be changed by that as well as what happens to them within the functon. For example, if I had a variable called "PotsAndPans" again, but it was global this time, and I did this to it outside of the function:


PotsAndPans=50


and then in the function I did this:


PotsAndPans=15


Then "PotsAndPans" would turn out to be 15, because it is global. The same applies to Arrays, but Arrays are ALWAYS global.

Alright, time for one of my favorite things about functions: you can pass variables into them! Remember how we were always passing numbers into functions? Well, we can also pass the contents of a variable into a function! Say we had our MakeTallRedBox function again. It would be like this:


Function MakeTallRedBox(OBJECT , HEIGHT)
Make Object Box OBJECT,10,HEIGHT,10
Color Object OBJECT,rgb(255,0,0)
ghost object on OBJECT
endfunction


And we could call it like this:


MakeTallRedBox(1,60)


That's one way you could do it. Another way is that you could also use variables! Say we wanted whatever was in the variable ObjectNumber to be the object number of out tall red box. To do that, you would do something like this:


ObjectNumber=3

MakeTallRedBox(ObjectNumber,60)


That would make a tall red box with an object number of 3 and a height of 60. Why an object number of 3? Because that's what is in that variable ObjectNumber that we passed into the function. Now, the contents of the variable OBJECT in our function is turned into the contents of the variable ObjectNumber that we passed in! Say we wanted to pass in a height variable as well. Then, we would do this:


ObjectNumber=3
VariableHeight=55

MakeTallRedBox(ObjectNumber,VariableHeight)


And it would make a tall red box with an object number of 3 and a height of 55.




And one last thing. It's sort of off topic, but oh well. There is one more command that you must be aware of. It's called EXITFUNCTION. It works kind of like the EXIT command for loops. It will forcibly leave the function before it's supposed to end. So, if you put it at the start of a function, it will leave the function before anything happens. so, calling this function:


function MakeACube(Object)
exitfunction
Make Object cube Object,10
endfunction


Would result in nothing, because you would have left the function before the cube was even made!

But like ENDFUNCTION, you can put a return value on EXITFUNCTION as well. You'd do it in the same way as you would ENDFUNCTION. Here's an example of EXITFUNCTION returning a value:


function Add(One,Two,Three)
Sum=One+Two
exitfunction Sum
Sum=One+Two+Three
FinalSum=Sum
endfunction FinalSum


That function would return the sum of the first two numbers because it wouldn't have gotten the chance to add all of the numbers, just the first two would have been added.




A FEW LAST NOTES:
-Arrays can be passed through functions and be changed, because they are always gloabl
-Global variables (only in DBP) can be passed through functions and be changed.
-TYPES (DBP) cannot be declared in functions.
-Arrays CAN be declared in functions.
-When decclaring a function, it's best to do it after all of your loops are done. You should declare all functions in that same area, one by one. They should get declared somewhere where they will not gone over by the compiler or the thing that reads your code. Function declarations should not be run. However, you SHOULD run functions calls. Treat function calls like normal commands.

EXAMPLES

=Only works in DBPro.
=Works in DBPro and DBC.

Some of the responses contain additions to this tutorial.

- Global Variables And Functions





- Arrays and Functions (similar to global variable example)





- Tall Red Box I



EDIT: Alright, more examples:

Putting strings into functions.



I hope this helped!


P.S. SEE TDK MAN'S POST FOR MORE INFO.

Jrock
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Posted: 25th Aug 2006 00:49 Edited at: 25th Aug 2006 00:50
Excellent Job Sixty Squares! This defenitly increased my confidence when using Functions, keep up the good work!

Quote: "This isn't my best tutorial."


I wouldn't say its your worst either.

Jrock is pronouned Jay-Rock
Sixty Squares
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Posted: 25th Aug 2006 02:39 Edited at: 28th Oct 2006 14:15
Haha thanks

Tutorials:
Array
Functions
Daemon
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Posted: 25th Aug 2006 03:07
Your tutorial is good, but you forgot recursives.

Factorials is a good example for it-


Sixty Squares
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Posted: 25th Aug 2006 04:02 Edited at: 25th Aug 2006 04:02
What's a recursive? Could you kindly add it to this tutorial?

Latch
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Posted: 25th Aug 2006 05:12
Another good Tutorial! You're on a roll!

The limit for number of parameters (at least in DBC) is 255.

It's possible to create and return complex structures (types?) in DBC as well using memblocks. I'm not sure if that would be concidered beyond the scope of this tutorial.

Enjoy your day.
Daemon
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Posted: 25th Aug 2006 05:26
A recursive is a function calling itself. You ofcourse wouldn't want this to go on forever, but occasionally it has a use.

Factorials are a good example. The factorial of 5 is 5*4*3*2*1=120. This is what the function I posted does.

SimSmall
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Posted: 25th Aug 2006 14:54 Edited at: 25th Aug 2006 15:12
May I add a bit please? The exitfunction command, leaves the function early if encountered. Exit function can also return data like:

(Here's one of my functions from VB converted to work in DB, showing how you might use an exit function.)



Plus, a global variable in DBC is declared by typing:
dim TestVariable(0)

Single dimension, single entry - but unlike DBP, you have to include the (0) each time, which can be frustrating...

Edit: showing it action...

print "You are in " + str$(Position) + RankSuffix(Position) + " place..."

So Rank 1 would read "You are in 1st place..."
Rank 12 would read "You are in 12th place..."
Rank 23 would read "You are in 23rd place..."
Rank 102 would read "You are in 102nd place..."
and yes, Rank 0 would read "You are in 0th place..."

Edit again: Not supposed to be spaces in endfunction and exitfunction
Sixty Squares
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Posted: 25th Aug 2006 15:51 Edited at: 25th Aug 2006 16:13
@SimSmall: Ah I forgot about that one (exitfunction) Thanks I added exitfunction to the tutorial.

@Daemon: Ah thanks, I didn't know you could do that.

@Latch: Thanks! But I'm afraid I cannot answer that one. Not sure if DBC supports types, but in DBPro you could make a type global and then modify it in the function, thus allowing you to sort of work around the one return value thing. I know nothing about memblocks.

Dracula
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Posted: 4th Oct 2006 18:54
very nice! Thank you for this info. Passing variables and arrays had always been troubling for me. No longer!!
Sixty Squares
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Posted: 28th Oct 2006 04:01
Woah sorry for the late response Dracula! It didn't tell me you had responded! Well, I'm glad that this helped you out

P.S. *bump*

Ummm...
Code Dragon
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Posted: 28th Oct 2006 04:41 Edited at: 28th Oct 2006 04:41
The fibonacci sequence is also a good example of recursive functions, but it's so ineffecient it's more an example of what not to use recursive functions for.



Confucius Say...
indi
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Posted: 28th Oct 2006 09:31
officially worth a proud sticky mate.

Sixty Squares
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Posted: 28th Oct 2006 14:08
@Code Dragon: Alright then

@indi: Thanks a bunch! I've never had a sticky before

Ummm...
Cave Man
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Posted: 2nd Nov 2006 22:19
Another great tutorial. I think this deserves to be stickied. Anyways, keep up the good work! This is a great tutorial for the newbies!

Sixty Squares
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Posted: 3rd Nov 2006 00:01 Edited at: 3rd Nov 2006 00:02
Thanks

Tutorials:
Array
Functions
dark donkey
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Posted: 11th Nov 2006 11:03
nice tutorial now! do! one! on! arrays!

http://www.darkdonkeygraphics.tk

Sixty Squares
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Posted: 11th Nov 2006 13:11
@dark donkey: Thank you! And guess what- I have already done one on arrays (see my signature).

Tutorials:
Array
Functions
dark donkey
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Posted: 11th Nov 2006 16:29
o yea thanks alot i have no idea on arrays excpept there like more than 1 varible

http://www.darkdonkeygraphics.tk

TDK
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Posted: 21st Dec 2006 04:54 Edited at: 21st Dec 2006 04:56
Quote: "That "DoComplexMath" function returns a REAL number or a FLOAT (notice the "#" sign after the variable name Answer"). "


Sorry, but that's not true. Just putting a # on the end of the receiving variable in a function call or the return value at the end of a function does not make the return value a float.

It may be classed as nitpicking, but it's worth pointing out, (for clarity more than anything), that the example function:

Function DoComplexMath(N)
Answer#=N*5-3+9+(N/2)-(N/4)
endfunction Answer#

is not strictly speaking correct. Though it will work, (as in it won't create an error when you run it) it can be confusing to those new to programming as it doesn't return what it should do.

The function call expects a float value returned, but passes an integer (5), and the line:

Answer#=N*5-3+9+(N/2)-(N/4)

actually calculates and returns an integer. Even though it's stored in a float variable it's still an integer. (35 in DBC and 32 in DBP if N=5 - go figure)!

Answer# should therefore be Answer, or you should alter the above line to ensure that a float is generated correctly.

Just a small point I know...

Also, like with function names, you shouldn't use reserved words as variable names - like OBJECT. In your examples, it's not that important and doesn't affect anything, but any newcomers might think it's OK to do it with any reserved word - which in certain circumstances could cause them problems.

Apart from that, nice tutorial!

TDK_Man

Sixty Squares
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Posted: 21st Dec 2006 12:35
Thanks for that. I made a note of yor post at the end.

Don Malone
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Posted: 21st Jan 2007 14:24
Nice work on the tutorial, as if you did not know that by now. well written and very informative.

Making nothing for the third straight year.

Sixty Squares
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Posted: 21st Jan 2007 17:44
A response exactly one month later!

Thanks

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