# Functions

<div class="margin-3">
    <?php
    $students = ['Doe, John' => 'r0662335', 'Doe, Jane' => 'r0715283', 'Smith, Jeff' => 'r0622915'];

    $search = 'r0622915';
    echo in_array($search, $students) ? "<p> Student with r-number $search was found!</p>\n" : 
        "<p> Student with r-number $search was not found!</p>\n";
    ?>
</div>

<div class="margin-3">
    <?php
    asort($students);
    echo "<p> Students sorted by r-number: </p>\n";
    echo "<ul>\n";
    foreach ($students as $name => $student) {
        echo "<li> $student: $name </li>\n";
    }
    echo "</ul>\n";
    ?>
</div>

<div class="margin-3">
    <?php
    ksort($students);
    echo "<p> Students sorted by name: </p>\n";
    echo "<ul>\n";
    foreach ($students as $name => $student) {
        echo "<li> $student: $name </li>\n";
    }
    echo "</ul>\n";
    ?>
</div>

<div class="margin-3">
    <?php
    $testString = 'this is a random string to illustrate PHP string functions';

    echo "<p> \$testString = '$testString' </p>\n";
    echo "<p> Length of \$testString = " . strlen($testString) . "</p>\n";
    echo "<p> Position (first occurrence!) of 'is' in \$testString = " . strpos($testString, 'is') . "</p>\n";

    echo "<blockquote>Execute the statement <code>\$testString = ucfirst(\$testString);</code></blockquote>\n";
    $testString = ucfirst($testString);
    echo "<p> \$testString = '$testString' </p>\n";

    echo "<blockquote>Execute the statement <code>\$subString = substr(\$testString, strpos(\$testString, 'P'), 3);</code></blockquote>\n";
    $subString = substr($testString, strpos($testString, 'P'), 3);
    echo "<p> \$subString = '$subString' </p>\n";

    echo "<blockquote>Execute the statement <code>\$testString = str_replace('PHP', 'some', \$testString); </code></blockquote>\n";
    $testString = str_replace('PHP', 'some', $testString);
    echo "<p> \$testString = '$testString' </p>\n";

    echo "<blockquote>Execute the statement <code>\$words = explode(' ', \$testString); </code></blockquote>\n";
    $words = explode(' ', $testString);
    echo "<p> \$words = </p>\n";
    print_r($words);
    ?>
</div>
<hr>
<div class="margin-3">
    <?php
    $percentages = [64, 67.4598, 72.25, 76.9];
    ?>
    <p>Numbers with 2 decimal digits and , as decimal point:</p>
    <ul>
        <?php
        foreach ($percentages as $percentage)
            echo "<li>" . number_format($percentage, 2, ',', '.') . "</li>\n";
        ?>
    </ul>
</div>

<div class="margin-3">
    <?php
    $timestamp = mktime(0,0,0,12,25,2019); //25-12-2019, 0u00
    echo "<p> Christmas 2019 (" . date("d/m/Y", $timestamp) . ") falls on a " . date("l",$timestamp). "</p>\n";
    ?>
</div>
<div class="margin-3">
    <?php
    echo "<p> Now, we are " . date("D d-m-Y, H:i:s") . "</p>\n";
    echo "<p>" . mktime(date("H"),date("i"),date("s"), date("m"), date("d"), date("Y")) . " seconds have passed since January 1, 1970, 00:00:00 </p>\n";

    $within4weeks = mktime(0,0,0, date("m"), date("d") + 28, date("Y")); 
    echo "<p> Within 4 weeks, we are " . date("l d F 'y", $within4weeks) . "</p>\n";
    ?>
</div>

<?php
function writeMessage(){
    echo "<p> We hope you like this PHP course! </p>\n";
}

function writePersonalMessage($name){
    echo "<p> Dear $name, we hope you like this PHP course! </p>\n";
}

function writePersonalMessageWithDefault($name = 'Mr./Mrs.'){
    echo "<p> Dear $name, we hope you like this PHP course! </p>\n";
}

function subtractReduction20($price){
    $price *= 0.8;
}

function subtractReduction30(&$price){
    $price *= 0.7;
}

function average($number1, $number2){
    return ($number1 + $number2)/2;
}
?>

<div class="margin-3">
    <?php
    writeMessage();
    writePersonalMessage('John');
    writePersonalMessageWithDefault('Jane');
    writePersonalMessageWithDefault();

    $price = 1000;
    subtractReduction20($price);
    echo "<p> Price with 20% reduction = " . $price . "</p>\n";

    $price = 1000;
    subtractReduction30($price);
    echo "<p> Price with 30% reduction = " . $price . "</p>\n";

    echo "<p> Average of 10 and 100 = " . average(10, 100) . "</p>\n";
    ?>
</div>