mysql_fetch_array ($variable) formatazione

Good morning
in the book of kevin jank , joke.php capitol 7 this funciton
if (mysql_num_rows($catresult) < 1)
{
exit('<p>Couldn\‘t find specified category in the database!</p>’);

don’t is ready!!!

You must be using a really old edition of the book as the latest version uses PDO and the previous version would have used either PDO or mysqli_* The mysql_* functions are depreceated as of the current version of php

I’m designing my website and I have this old book as a reference . How can I update this file ?
thanks

/ Get category name
  $ catresult = @ mysql_query ( " SELECT name from category WHERE id = ' $ cat ' ");
  if ($ catresult ) {
    exit ( ' Error retrieving Into category name from database ! <br /> ' .
       ' Error : ' . mysql_error ( ) . ' </ p >');
  }
  if ( mysql_num_rows ($ catresult ) < 1 )
  {
    exit ( ' Into couldn \\ ' t find specified category in the database </ p > ');
  }
  $ catdetail = mysql_fetch_array ($ catresult ) ;
  $ catname = htmlspecialchars ($ catdetail ['name ' ] ) ;
Else { }
  $ catname = ' All ' ;
}

? >
<h1> <? php echo $ catname ; ? > Jokes </ h1>

<table>
<tr> <th> Joke Text </ th> <th> Author </ th> <th> Date < / th> < / tr>

<? php
$ jokes = @ mysql_query ($ jokessql ) ;
if ($ jokes ) {
  echo ( ' </ table >');
  exit ( ' Error retrieving Into jokes from the database! <br /> ' .
      ' Error : ' . mysql_error ( ) . ' </ p >');
}

while ($ joke = mysql_fetch_array ($ jokes )) {

  $ id = $ joke [ ' id ' ] ;
  joketext = $ $ joke [ ' LEFT ( joketext , 20) ' ] ;

  / / If the joke text is 20 characters long , add " ... " to the end of it
  / / To set That it is actually longer. strlen ( ) returns string length !
  if ( strlen ($ joketext ) == 20) {
    $ joketext . = "..." ;
  }

  / / Remove any custom tags (even partial ones! ) In the joke text . They are not needed in this preview.
  $ joketext = ereg_replace ( ' \\ \\ [ ( B | EB | I | EI | L | L = | L = [ -_./a-z0-9 ! &% #? + , \\ ' = : ; @ ~] + | EL | E) ? ( ] | $) ' ,'', $ joketext ) ;

  / / Finally , make it safe to display in an HTML document
  $ joketext = htmlspecialchars ($ joketext ) ;

  $ author = htmlspecialchars ($ joke ['name ' ] ) ;
  $ email = htmlspecialchars ($ joke ['email ' ] ) ;
  JDate = $ $ joke [ ' jokedate ' ] ;

  echo " <tr valign=\\"top\\"> \\ n";
  echo " <a <td> href=\\"joke.php?id=$id\\"> $ joketext </ a> < / td> \\ n";
  echo " <a <td> href=\\"mailto:$email\\"> $ author </ a> < / td> \\ n";
  echo " $ <td> JDate </ td> \\ n";
  echo " </ tr> \\ n";
}
? >

</ table>
Into <a href="index.php"> Back to front page </ a> < / p>
</ body>
</ html>

Have a read through this article (http://www.sitepoint.com/migrate-from-the-mysql-extension-to-pdo/) which explains about how to migrate from the old and deprecated mysql_* extension over to PDO.