php Form Validation help

have a form that I would like to validate before it is submitted to the DB. I am having trouble with a couple of sections. I have a select box with a listing of all the states, the first option is "Choose One" with a value of "0". Would this be the correct way to "validate" this field? <CODE> $state = $_POST['state']; if ($state = 0) { print '<p>Please select your State</p>'; } </CODE> Second, another part of the same form I have fields for phone numbers, once the field is submitted I would like to join the 3 sections of areacode, nxx and prefix. I have done this to join them, is this correct? <CODE> $phone = $_POST['p-areacode'] . - . $_POST['p-prefix']. - . $_POST['p-suffix']; </CODE> The next question id for both phone number and area code. If I want to validate the zip code and ensure a minimum of X characters in the field, numbers only how would I do this? Would this be somewhat on the right track? <CODE> If ($zip str >5) { print '<p>Please enter your Zip Code (EX. 77662)</p>'; } </CODE> And for the phone number I would assume I could use: <CODE> If ($_POST['p-areacode'] str >3 ) { print '<p>Please enter your Area Code (EX. 77662)</p>'; } </CODE> I am still new with PHP, any help would be appreciated. Below is the code I have sofar: