TechTip: Starting at the Beginning with PHP Arrays

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Learn about basic PHP arrays and how they're defined and looped.

 

If, like me, you have begun to use PHP in conjunction with RPG, you'll very soon be using the arrays in PHP. You are of course familiar with arrays in RPG, and arrays in PHP work almost the same except that there are more than 75 functions that can be used on arrays in PHP. When you start to dig into them, you'll wish that the compiler guys at IBM would start looking into them as well.

 

In this TechTip, I'll show you a few functions that I find very useful, which I'm sure will encourage you to look into this huge subject more deeply.

Defining Arrays and Looping in Arrays

When you start working with arrays in PHP, you'll notice that one thing is very different from RPG: PHP arrays are zero-based. That means that the first element in a PHP array is array element zero, and that's one of the main errors an RPG programmer encounters in the beginning.

 

There are three types of arrays in PHP:

 

 

  • Numeric arrayThis is an array with a numeric index as we know it from RPG.
  • Associative arrayThis is an array where each id key is associated with a value. This is not something we know from RPG, but it's very useful when you get the hang of it.
  • Multidimensional arrayThis is an array containing one or more arrays, and we know it from RPG. You can combine a data structure and an array and get the same functionality. These will be covered in a later TechTip.

 

When defining a PHP array, the syntax is like this:

 

array(key => value)

 

Parameter

Description

Key

The   key is optional. The key can be either numeric or string. If the key is not   set, an integer key will be generated, starting at 0 (zero-based).

Value

The   value is required. It specifies the value of the element.

 

 

Let's try to define a few arrays.

 

Example 1: Define a numeric array and print out the content.

 

<?php

 

// Define an array

$wrkAry = array("0"=>"Costello","1"=>"Cave","2"=>"Interpol");

 

// Print out the array

print_r($wrkAry);

 

echo "<hr>";

echo $wrkAry[0] . '<br>';

echo $wrkAry[1] . '<br>';

echo $wrkAry[2] . '<br>';

 

?>

 

 

As you can see in example 1, we define the array using the array() function, and then we fill the array using the key => value syntax.

 

We print out the whole array using the print_r() function and also print out the array using the echo function, specifying each array element starting with zero.

 

Example 2: Define an associative array and loop through it.

 

<?php

 

// Define an associative array

$wrkAry['a'] = "Elvis Costello";

$wrkAry['b'] = "Nick Cave";

$wrkAry['c'] = "Interpol";

$wrkAry['d'] = "The Police";

$wrkAry['e'] = "Sea Pink";

 

echo "<hr>";

echo "Associative Array - \"foreach\" loop";

echo "<hr>";

 

// Loop through the array using foreach

foreach ($wrkAry as $key => $value) {

   echo 'Key: ' . $key . ' / Value: ' . $value .'<br>';

}

 

?>

 

In example 2, we define an associative array, which means that the index value is a stringin this, case a to e. It could have been anything, such as names or months.

 

To loop through the array, we use the foreach function. This way of looping gives us access to both the value and the key. You can see the syntax in the example.

 

Of course, you can also loop through an array like you do in RPG, but this way, the array must be numeric, as shown in example 3.

 

Example 3: Loop through a numeric array using a for loop.

 

<?php

 

// Define a numeric array

$wrkAry[0] = "Elvis Costello";

$wrkAry[1] = "Nick Cave";

$wrkAry[2] = "Interpol";

$wrkAry[3] = "The Police";

$wrkAry[4] = "Sea Pink";

 

echo "<hr>";

echo "Numeric Array - \"for\" loop";

echo "<hr>";

 

// Loop through the using a for loop

for ($i=0; $i<=count($wrkAry)-1; $i++) {

echo "The key is: $i / The value is: $wrkAry[$i] <br>";

}

 

 

?>

 

In example 3, we use a "normal" for loop as we know it in RPG (and JavaScript for that matter). Note that we use the count() function to find the number of elements in the array. Also note that we subtract 1 because the array is zero-based and the count() function will return the value 5, so to avoid a PHP error, we subtract one to make the loop work.

Just the Beginning

This is just the beginning, and you can download the code here. In upcoming issues of TNT, I'll show you some more PHP array examples that will make your PHP programming life a little easier I hope. You'll be wondering, "Why don't we have that in RPG?"

 

And, yes, I know that I still owe you another "jQuery Fundamentals" TechTip. I'm working on that, and you'll see it soon.

 

Till then, I wish you all a happy new year.

 

 

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