PHP is a weakly-typed language. It does not require explicit declaration of data types. The context in which the variable is used determines its data type; conversion is done automatically:
$a = "2"; // string
$a = $a + 2; // integer (4)
$a = $a + 0.5; // float (4.5)
$a = 1 + "2 oranges"; // integer (3)