Stopping certain characters from a form???

[TheMayhem]

On my little form input I have discovered a nasty bug. I basically want the user to input numbers 0-9 only and want to make it so that if a user enters a * or / or - or + that it will give them the error, what is the best way from disabling these characters from an input field?

[kburger]

is_numeric()

[bradgrafelman]

If you only want single digits 0-9 (not 10, for example):

if(!ereg("^[0-9]$", $_POST['number_field'])) {
  // What to do if they did NOT enter only numbers!

} else {

  // What to do if they DID enter only numbers!

}

If, however, you want to make sure they entered a number (i.e. just any number, not a single digit number), use is_numeric() like kburger suggested.

NOTE: This code is UNTESTED, as I am at school right now instead of at home.