for,foreach遍历数组

<?php
$arr_1 = array(1,"zhangsan",25);//下标为数字的一维索引数组，可以用for循环遍历
$arr_2 = array("id"=>2,"name"=>"lisi","age"=>28);//一维关联数组，不能用for循环遍历
//下面是二维关联数组
$arr_3 = array(array("id"=>2,"name"=>"lucy","age"=>26),
array("id"=>3,"name"=>"lili","age"=>27),
array("id"=>4,"name"=>"lisi","age"=>28),
);
//一维索引数组可以用for循环遍历出数组内容
for ($i=0; $i <count($arr_1) ; $i++) {
echo $arr_1[$i]."  ";
}
/*
1  zhangsan  25
*/
echo "<hr/>";
//一维索引数组还可以用foreach循环遍历出数组内容
foreach ($arr_1 as $key => $val) {
echo $val."<br/>";
}
/*
1
zhangsan
25
*/
echo "<hr/>";
//一维关联数组不能用for循环，只能用foreach
foreach ($arr_2 as $key => $val) {
echo $key."-->".$val."<br/>";
}
/*
id-->2
name-->lisi
age-->28
*/
echo "<hr/>";
//二维关联数组用foreach循环遍历
foreach ($arr_3 as $val) {
echo $val['id']."  ";
echo $val['name']."  ";
echo $val['age']."<br/>";
}
echo "<hr/>";
/*
2  lucy  26
3  lili  27
4  lisi  28
*/

//二维关联数组用foreach循环2次遍历
echo '<table border="1" width="20%" align="center" cellpadding="0" cellspacing="0" align="center">';
echo '<tr><th>ID</th><th>NAME</th><th>AGE</th></tr>';
foreach ($arr_3 as $key=>$row) {
echo "<tr>";
if(is_array($row)){
foreach ($row as $col) {
echo "<td align='center'>".$col."</td>";
}
}else{
echo "<td >".$key.':'.$row."</td>";
}
echo "</tr>";
}
echo "</table>";
?>