shyzwbtk…

2. That is a real pitfall, only using (int) casting or using intval() saves the day!

3. Good to know, thanks.

4. In first place, if foreach gets at least 1 iteration, everything will be ok. Otherwise the array will be NULL which can lead to serious problems.

5. $_GET, $_POST and $_REQUEST are dangerous. Everybody should be trained to use them correctly!

6. mysql_real_escape_string is only necesary if you have strings, numbers and floats can be “validated” by simply casting them (int)$number;

7. A pitfall for beginners. Every devolper should use error_reporting(E_ALL); while developing.

8. strpos is the functions beginners need to learn that == is not ===.

Thanks for this list, hope much people will read and use it!