why people are defining data type in php?

Hi friends why people are defining data type in php as below,

$id 开发者_StackOverflow= (int) $_GET['id']; 

---

To make sure the variable really contains a valid number. For example, empty string will be converted to 0, 'abc' will be converted to 0, etc.

---

This assigns the value of the URL parameter "id" (converted to an integer) to the variable $id. The parameters in the URL are of course strings, therefore if you pass an integer this way you first should cast it to the int datatype.

---

Because that way you know what you are manipulating so there is no surprise.