<?php
$a = 'hello';
?>

<?php
$$a = 'world';
?>

<?php
echo "$a ${$a}";
?>

<?php
echo "$a $hello";
?>

<?php
class foo {
  var $bar = 'I am bar.';
  var $arr = array('I am A.', 'I am B.', 'I am C.');
  var $r  = 'I am r.';
}
$foo = new foo();
$bar = 'bar';
$baz = array('foo', 'bar', 'baz', 'quux');
echo $foo->$bar . "\n";
echo $foo->$baz[1] . "\n";
$start = 'b';
$end  = 'ar';
echo $foo->{$start . $end} . "\n";
$arr = 'arr';
echo $foo->$arr[1] . "\n";
echo $foo->{$arr}[1] . "\n";
?>

<?php
 //You can even add more Dollar Signs
 $Bar = "a";
 $Foo = "Bar";
 $World = "Foo";
 $Hello = "World";
 $a = "Hello";
 $a; //Returns Hello
 $$a; //Returns World
 $$$a; //Returns Foo
 $$$$a; //Returns Bar
 $$$$$a; //Returns a
 $$$$$$a; //Returns Hello
 $$$$$$$a; //Returns World
 //... and so on ...//
?>

<?php
// Given these variables ...
$nameTypes  = array("first", "last", "company");
$name_first  = "John";
$name_last  = "Doe";
$name_company = "PHP.net";
// Then this loop is ...
foreach($nameTypes as $type)
 print ${"name_$type"} . "\n";
// ... equivalent to this print statement.
print "$name_first\n$name_last\n$name_company\n";
?>

/**
 *计算两个数的和，并返回计算的结果
 * @param number $a
 * @param number $b
 * @return number
 */
function sum($a, $b){
  return $a + $b;
}

/**
 *计算两个或三个数的和，并返回计算的结果
 * @param number $a
 * @param number $b
 * @return number $c 该参数可以不传入值,默认为0
 */
function sum($a, $b, $c = 0){
  return $a + $b + $c;
}

/**
 *计算任意多个数的和，函数参数params必须为array类型
 * @param array params
 */
function sum($params){
  $total = 0;
  foreach ($params as $i){
    $total += $i;
  }
  return $total;
}

$age = 18;
var_dump($age); //显示变量$age的详细信息

$name = '张三';
$age = 18;
$gender = true;
var_dump($name, $age, $gender);

/**
 *计算任意多个数的和，并返回计算后的结果
 */
function sum(){ //这里的括号中没有定义任何参数
  $total = 0;
  //使用func_get_args()来获取当前函数的所有实际传递参数，返回值为array类型
  $varArray = func_get_args();
  foreach ($varArray as $var){
    $total += $var;
  }
  return $total;
}
/*****下面是调用示例*****/
echo sum(1, 3, 5); //计算1+3+5
echo sum(1, 2); //计算1+2
echo sum(1, 2, 3, 4);  //计算1+2+3+4

/**
 *计算任意多个数的和，并返回计算后的结果
 */
function sum($a, $b){
  return array_sum(func_get_args());
}