Convert if else to try catch - php

Question

Can somebody help me in converting the following code written using if-else to try/catch. Also let me know is trycatch needed in this case or if-else is apt
$results = mysql_query($query);
if(mysql_num_rows($results)!=0)
{
while(($result = mysql_fetch_row($results))!=FALSE)
{
$res ="DELETE FROM table1 WHERE id ='".$result['id']."'";
if(mysql_query($res)==false)
{
echo mysql_error();
exit;
}
}
echo $res ="DELETE FROM table2 WHERE id ='".$id."'";
if(mysql_query($res)!==false)
{
header("Location:list.php?m=4");
}
else
{
echo mysql_error();
exit;
}
}
else
{
echo "Error";
}

Answer 1

try...catch only makes any sense if your functions are throwing exceptions. If they don't, there's nothing to catch. I'd start with this as a refactoring:
$results = mysql_query($query);
if (!mysql_num_rows($results)) {
echo 'No results!';
exit;
}
$ids = array();
while (($result = mysql_fetch_row($results)) !== false) {
$ids[] = $result['id'];
}
$ids = array_map('mysql_real_escape_string', $ids);
$query = "DELETE FROM table1 WHERE id IN ('" . join("','", $ids) . "')";
if (!mysql_query($query)) {
echo mysql_error();
exit;
}
$query = "DELETE FROM table2 WHERE id = '$id'";
if (!mysql_query($query)) {
echo mysql_error();
exit;
}
header("Location: list.php?m=4");
exit;
This can still be improved a lot, but it's already an improvement over your spaghetti logic. If you're seriously interested in properly using exceptions, you should first move on to properly using functions for repetitive tasks (like the error, exit parts), then possibly restructure the whole thing into classes and objects, and lastly use exceptions to communicate between the now nested layers. Maybe start using a PHP framework to get a feeling for the whole thing.
Putting exceptions into the above code would be hardly more than a goto, but just for illustrative purposes:
try {
$results = mysql_query($query);
if (!mysql_num_rows($results)) {
throw new Exception('No results!');
}
$ids = array();
while (($result = mysql_fetch_row($results)) !== false) {
$ids[] = $result['id'];
}
$ids = array_map('mysql_real_escape_string', $ids);
$query = "DELETE FROM table1 WHERE id IN ('" . join("','", $ids) . "')";
if (!mysql_query($query)) {
throw new Exception(mysql_error());
}
$query = "DELETE FROM table2 WHERE id = '$id'";
if (!mysql_query($query)) {
throw new Exception(mysql_error());
}
header("Location: list.php?m=4");
exit;
} catch (Exception $e) {
echo 'ERROR: ' . $e->getMessage();
exit;
}

Answer 2

from the sound of it, it seems you think try/catch and if-else as the same behaviour. That is not the case. Try catch is used to prevent an exception from making the application crash or to handle exceptions gracefully, and to perform logging and giving user feedback. If-else (else if) is used to check the internal state of your application, and perform different actions accordingly.
Generally, a try-catch is less efficient than if there is a switch-case or else-if approach to the problem.