gettype(variable);

$int = 10;
echo gettype($int)."\n"; // outputs:  integer

$str = "PHP";
echo gettype($str)."\n"; // outputs:  string

$flt = 1.2;
echo gettype($flt)."\n"; // outputs:  double  (also called float)

$bool = true;
echo gettype($bool)."\n"; // outputs:  boolean

$arr = [1,2,3,4,5,6,7,8,9,10];
echo gettype($arr)."\n"; // outputs:  array