Numeric input validation in PHP
<p>I'm trying to validate an input for Account number in php form. It should contain 8 numbers and '-' optionally. If there is '-' - it should be ignored. 
After pressing the Submit button, the warning message suppose to be displayed above the form in case input is invalid.</p>

<p>Please help. </p>

<p>This is what I got so far, but I'm  not sure if this is correct and don't know how to display a warning message above the form. </p>

<pre><code>$acctnum= "$acctnum";

if(empty($acctnum)){
  echo "You did not enter an account number, please re-enter"; }

else if(!preg_match("\-^[0-9]{8}", $acctnum)){
  echo "Your account number can only contain eight numbers. Please re-enter."; }
</code></pre>

<p>Thank you!</p>
