PHP in_array函数不起作用

Question

I have some problems with in_array() I want to create a unique number from 100-999 that is not stored in the array already, but the in_array function does not seem to work. The example below is what my code is right now.

I have pushed 2 strings to the array in the top. In the function, I try to run it, but just get the value "sb100", and I should get "sb102" because 100 and 101 are already in the array.

$uniqueIDs[] = "sb100";
$uniqueIDs[] = "sb101";

function keyExists($ui){
    for($i=100;$i<=999;$i++){
        $R = "sb".$i;
        if(in_array($R, $ui)){
            return "";
        }else{
            return $R; 
            break;
        }
    }
}    

keyExists($uniqueIDs);

Answer 1

The problem is that as when it finds an element that already exists, it does return "";. Instead you just continue if it's in the array and return if it isn't the array...

function keyExists($ui){
    for($i=100;$i<=999;$i++){
        $R = "sb".$i;
        if(!in_array($R, $ui)){
            return $R;
        }
    }
}