Where can you get a good "functions" tutorial?

[faydra92]

i just need to know how to structure them, what variables they have access to and any other tidbits thats one would need to know when using functions 🙂

[cgraz]

check here under Programming

Cgraz

[drew010]

I'll see if I can give you a small rundown on them here:

Functions are a way to easily be able to re-use code and organize your programs better. They are very simple to use and help greatly, lol i already sound liek a textbook...

The basic function definition in php looks like this:

[B]function[/B] functionName ([I]optional_args[/I]) {
     <code>
}

Lets take that and make a function that draws a rectangle:

function drawQuadrilateral() {
     echo "****************<br>\n";
     echo "*              *<br>\n";
     echo "*              *<br>\n";
     echo "****************<br>\n";
}

Now, if you
echo drawQuadrilateral();
you will see all those *'s print out in that shape.

However that is not very flexible and easy to change, lets make the same function but have it take on arguments (parameters) to make the dimentions.

function drawQuadrilateral($height,$width)
{
        for($current = 0; $current < $width; $current++) {
                echo '*';
        }
        echo "<br>";

    for($col = 0; $col <= $height - 2; $col++) {
            echo '*';
            for($row=0; $row < $width * 2 - 4; $row++) {
                    echo '&nbsp;';
            }
            echo "*<br>\n";
            }
            for($current = 0; $current < $width; $current++) {
                    echo '*';
            }
    echo "<br>";
}

now try
echo drawQuadrilateral(5,30);
and
echo drawQuadrilateral(10,15);
and see the output..

How about a function that returns a value: These are very easy..
Here is a function that will calculate the sum of squares from a number down to 1. i.e. if they enter 5, it will calculate 55 + 44 + 33 + 22..

function sumSquares($number)
{
     for ($current = $number; $current >= 1; $current--) {
            $sumSquares = $sumSquares + ($current * $current);
     }
     return $sumSquares;
}

As you can see, these functions are not too hard...with return functions, you can return any kind of data-type, arrays, booleans, ints, floats, etc...

Lets close with a few notes:

What variables are accessable to functions?
The simple answer is: none. Only variables which are passed into functions thru parameters are accessable, but there is a way around this. In PHP, all variables outside of different functions are kept in the $_GLOBAL array. So right inside the function, you can get variables to be accessable from within. To do this, simply put
global $varname, $varname2, $varname3...;
Then those variables are accessable to the function without being passed in.

Now you may wonder, if you have seen on the php manual or in functions where there are optional variables that you can enter if you choose but are not mandatory. This is done by creating a default value for them in the function definition. See the following:

function optionalVars($height, $width, $color = "#ff0000") {
...

With a function like that, you can call it in multiple ways
First like
optionalVars(5,12);
or
optionalVars(5,12,"#ff00ff");

either will work and if the third parameter is blank, it will default to #ff0000.

For more information on functions, see the official php.net website documentation on functions located at http://php.net/manual/en/functions.php

If you have more questions feel free to email or post back....i hope that helped you out some..

[faydra92]

but why do you 'echo function();'?

and not function();?

in the function, youre already echoing, so one would assume that if you call the function it would echo whats in it

why do you use echo function();? and not function();??

[drew010]

in this case echo will work the same as just putting the function call without echo...
but echoing value returning functions is necessary for it to show the result or the return.

[faydra92]

thanks 🙂

and also, what variables do functions have access to?

if i have

<?
$test = "hello";

function something() {
echo $test;
}
?>

im pretty sure that will echo nothing... right?

how can i set $test to be a variable that the function can read?

[drew010]

you are right, if you echo $test in the function, nothing will show. that is kinda the last thing i covered in the post... but here is how to do it.

<?
$test = "hello";

function something() {
global $test;
echo $test;
}
?>

after adding global, now test will be available to the function. You can add multiple variables by seperating them with commas, for example
global $test,$test2,$test3;

[DeltaRho2K]

Obviously, these examples are very basic, but good practice to see how to implement things... Here are a couple of other ways to get your variables into your functions...

<?
$test = "Something";

function something($test) {
echo $test." ";
}

something($test);


function somethingelse($test2 = "else") {
echo $test2;
}

somethingelse();

?>

By the way drew, I enjoyed your quick lesson... Good info for a refresher course on the basics of the most difficult principles, is always a great thing!

[faydra92]

<?
function test($somestring){
echo $somestring;
}
$somestring = "wtf";
test();
?>

that doesnt work.. any idea why?

Warning: Missing argument 1 for test() in /usr/home/vaxop/biggiemovies.com/test.php on line 2

[drew010]

that variable you declare before the function is a global variable and the other functions dont have access to it.

then you call the function test, which requires one argument and you are not passing in.

if you do
test("wtf");
the value $somestring inside test gets wtf. remember, you either MUST pass the variables in as arguments, OR use the reserved word global followed by the variables you want the function to have acccess to.

[faydra92]

still doesnt work

global $a;
function test(){
    echo $a;
}
$a = "echo this please";
test(); 

echos nothing

[drew010]

global has to be INSIDE the function that you want to access the variable, not before it..

function test()
{
global $test;
echo $test;
}

NOT

global $test;
function test()
{
echo $test;
}

good luck with it, feel free to email or post back for more help...

[codeDV]

Think of a function as a mini PHP script. The basic function will have:

Input --> Process -> Output

function add ($num1, $num2) {
  $ret = $num1 + $num2;

  return $ret;  

}

You use function arguments to pass your input:

// function call
$result = add (3, 2);

Your process is anything which happens between the braces {} and before the word return is encountered:

  $ret = $num1 + $num2;

And your output is the result of your process. You can pass control back to your script and return a value using the return statement. This returned value can be assigned a variable, as you can see above:

  return $ret;

Functions don't have to return their output using the return statement. They could output text to the browser, or access and change files:

function bold ($text) { // input
  // process
  $output = "<b>" . $text . "</b>";

  // output
  echo ($ouput);
}

That one makes text bold and sends the processed text straight to the browser.

// function call
bold ("I am bold text.");

The input passed to the function is always done so by its value. This means that you can stick expressions in your functions input too:

function squared ($num) { // input
  // process
  $ret = $num * $num;

  // output
  return $ret;
}

// function call
$result = squared (3 + (2 * 4));

You can also use the functions return value as part of an expression:

// function call inside an expression
$result = $num + squared (3 + (2 * 4));

What if you want a function to modify its input as well as return a value? This is where passing by reference comes in. Instead of passing an (argument) input as a value you can pass the location of a variable in your main PHP script allowing the function to modify it directly:

function get_text_file ($path,  &$status) { // input

  $status = true; // set initial; value

  // process
  $fp = @fopen ($path, "r"); // open file for reading

  if (! $fp) {
    $status = false;
    return;
  }

  $contents = @fread ($fp, filesize ($path)); // read the entire file
  fclose ($fp); //close file

  return $contents;
}

As you can see the (&) in the functions argument status causes the variable to be passed by reference. You cannot use expressions when passing by reference. Here's a typical use of the above function:

$file = get_text_file ("test.php", $success);

if ($success)
  echo ($file);
else
  echo ("There was an error.");

This is only a small example of how functions can be used. There are so many ways in which you can utilise them. what I suggest is you learn the basics from the PHP Documentation, then experiment by copyiing their examples and observing how they work.