How to check if a field is not empty and with allowed caracters in an PHP function? -

i want better on not nesting if-satments , got brother how think. thougt here create function validates fields in form filled in , allowed caracters.

but i'm expert on nested if:s , need learn better way of doing it. question how can same check in function instead? can use practise? can array?

my nested if statment here (i'm supposed bigger form later on):

// if submit button has been clicked if(isset($_post["login"])){      // checks if username-field empty , if allowed characters used     if(empty($_post['user']) or !preg_match("/^[a-za-z0-9 ]*$/", $_post['user'])){         $error = "you can't leave field empty , can use letters, numbers , space.";     }else{         // checks if password-field empty , if allowed characters used         if(empty($_post['pass']) or !preg_match("/^[a-za-z0-9 ]*$/", $_post['pass'])){             $error = "you can't leave field empty , can use letters, numbers , space.";         }else{             // code here         }     } } 

and base want try instead:

function validate(){     // code here }  // if submit button has been clicked if(isset($_post["save"])){        if(validate(/*vaibles each of fields in form*/)){      }else{      } } 

as asked example, check this:-

<?php if(isset($_post["login"])){     $error = validate($_post);      if(empty($error) {      .....//your further processing code     }else{      // code show error @ appropriate place.     } } function validate($dataarray){     $validatearray  = $dataarray; // either asign new variable or can use directly $dataarray     $errors = array();     if(empty($_post['user']) or !preg_match("/^[a-za-z0-9 ]*$/", $_post['user'])){         $errors['user'] = "you can't leave field empty , can use letters, numbers , space.";     }     if(empty($_post['pass']) or !preg_match("/^[a-za-z0-9 ]*$/", $_post['pass'])){             $errors['pass'] = "you can't leave field empty , can use letters, numbers , space.";      }      //......so on      return $errors; } ?> 

note:- example how can proceed. thanks.