PHP and Array in if statements

I have an array of zeros like this:

$a = array(0 , 0 , 0 , 0 );

I want an if statement that is about like this:

if ($a == 0){
    //do something;
}else{
    //do not do something!!!;

How can it be possible? with foreach? how? i think the answer is this:

$size = sizeof($a);
for($i=0 ; $i < $size ; $i++){
    if( $a[$i] != 0){
    break;
    }else{
    //do something
}

but for a big array i think it may fags the CPU is there other way?