PHP 字符串输出 echo、print 与 printf 函数

[php]代码库

<?php 
$foo = "foobar"; 
$bar = "barbaz"; 
echo $foo,$bar;     // 输出"foobarbarbaz" 
echo "<br />"; 
echo $foo[3];       // 输出第4个字符"b" 
echo "<br />"; 
echo "foo is $foo"; // 输出"foo is foobar" 
echo "<br />"; 
echo 'foo is $foo'; // 输出"foo is $foo" 
?>