PHP code reuse and functions

<?php
//使用require()、include()函数
echo &#39;This is the main file.<br/>';
require('reusable.php');
echo 'The script will end now.<br/>';
//函数声明
function my_function(){
    echo 'My function was called';
}
my_function();
//使用参数
function create_table($data){
    echo "<table border=\"1\">";
    reset($data);
    $value=current($data);
    while($value){
        echo "<tr><td>".$value."</td></tr>\n";
        $value=next($data);
    }
    echo "</table>";
}
$my_array=array('Line one','Line two','Line three');
create_table($my_array);
//作用域 关键字global
function fn(){
    global $var;
    $var="contens 2";
    echo "inside the function,\$var =".$var."<br/>";
}
$var="contents 1";
fn();
echo "outside the function,\$var =".$var."<br/>";
//参数的引用传递和值传递：地址符&
function increment(&$value,$amount=1){
    $value=$value+$amount;
}
$a=10;
echo $a.'<br/>';
increment($a);
echo $a.'<br/>';
//return关键字：终止函数的执行
function larger($x,$y){
    if((!isset($x))||(!isset($y))){
        echo "This function requires two numbers.<br/>";
        return;
    }
    if($x>=$y){
        echo $x."<br/>";
    }else{
        echo $y."<br/>";
    }
}
$a=1;
$b=2.5;
$c=1.9;
larger($a,$b);
larger($d,$a);
//return关键字：从函数返回一个值
function smaller($x,$y){
    if((!isset($x))||(!isset($y))){
        return false;
    }else if($x<=$y){
        return $x;
    }else{
        return $y;
    }
}
echo smaller($a,$b).'<br/>';
echo smaller($d,$a).'<br/>';
//实现递归
function reverse_r($str){
    if(strlen($str)>0){
        reverse_r(substr($str,1));
    }
    echo substr($str,0,1);
    return;
}
function reverse_i($str){
    for($i=1;$i<=strlen($str);$i++){
        echo substr($str,-$i,1);
    }
    return;
}
reverse_r('hello');
echo '<br/>';
reverse_i('hello');
//phpinfo();