php文章tag标签的增删

<?php
session_start();

if ( $_POST ){

    $_SESSION [ 'old' ]= array ( 'one' , 'two' , 'three' , 'four' , 'five' );
    $_SESSION [ 'old' ]= array ();
    $_SESSION [ 'old' ]= array ( 'two' , 'five' );

    $new =( array )  $_POST [ 'big' ];
    foreach ( $new  as  $k => $v ){
        if (!in_array( $v , $_SESSION [ 'old' ])){
            $_SESSION [ 'old' ][]= $v ;
            echo  'add ' . $v ;
            echo  '<br />' ;
        } else {
            echo  'mod ' . $v ;
            echo  '<br />' ;
        }
    }
    foreach ( $_SESSION [ 'old' ]  as  $k => $v ){
        if (!in_array( $v , $new )){
            $id = array_keys ( $_SESSION [ 'old' ], $v );
            unset( $_SESSION [ 'old' ][ $id [0]]);
            echo  'del ' . $v ;
            echo  '<br />' ;
        }
    }
    echo  "<pre>" ;
    print_r( $_SESSION [ 'old' ]);
}
?>

<form method= "post" >

<input type= "checkbox"  name= "big[]"  value= "one"  /> one<br />
<input type= "checkbox"  name= "big[]"  value= "two"  /> two<br />
<input type= "checkbox"  name= "big[]"  value= "three"  /> three<br />
<input type= "checkbox"  name= "big[]"  value= "four"  /> four<br />
<input type= "checkbox"  name= "big[]"  value= "five"  /> five<br />
<input type= "submit"  value= "submit"  name= 'abc' >
</form>