php如何在数组中查询某个值

<?php

$a=array("a"=>"Dog","b"=>"Cat");
if(array_key_exists("a",$a)){
    echo "Key exists!";
}else{
    echo "Key does not exist!";
}

$a=array("a"=>"Dog","b"=>"Cat","c"=>5,"d"=>"5");
echo array_search("Dog",$a);
echo array_search("5",$a);
?>