php switch statement limit - php

Question

PHP script that I'm using contains the switch statement and break to prevent the code from running into the next case automatically:
if (!isset($a)) $a = '';
switch($a)
{
case 1:
default:
// some code
break;
case 2:
// some code
break;
case 3:
// some code
break;
}
How can I prevent users to write in URL as "$a" some number that does not exist in php switch statement?
For example, in this example above, if someone writes as a url indes.php?a=5 should get a message that the link is not correct. What is the best way to do that?
Another thing that interests me, is there any limit on the number of switch statements that it is wise to use on one page or can the size of that page can cause the problem if it is to too large?

Answer 1

Add this to the end of the switch.
default:
echo 'not correct';
break;

Answer 2

From php docs:
A special case is the default case. This case matches anything that wasn't matched by the other cases. For example:
<?php
switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
default:
echo "i is not equal to 0, 1 or 2";
}
?>
http://php.net/manual/en/control-structures.switch.php

Answer 3

Add the default case.
default:
echo 'Invalid Option';
break;
And there is no limit for the cases in switch.
Update:
No matter what ever the size of the page is. But surly it depends on the script or code written inside the cases. It it is time consuming than that will effect.

Answer 4

The placement of your default tag might be causing an issue, but I'm not 100% sure of this:
if (!isset($a)) $a = '';
switch($a)
{
case 1:
default:
// some code
break;
case 2:
// some code
break;
case 3:
// some code
break;
}
The individual case statements execute whenever there is a match with $a. For example if the user submitted 3 (thus $a==3), then case 3 would execute. It will continue to execute until the break; statement is hit. The default block is only executed if no case statements match the value contained in $a.
For example if the user submitted 5 (thus $a==5), there is no case 5: so the default block would be executed. Thusly, it's usually a standard practice to place your default: block at the end of your switch statement as follows to show that if no case statements match the condition, it will be executed last.
if (!isset($a)){
$a = '';
}
switch($a)
{
case 1:
//some code
break;
case 2:
// some code
break;
case 3:
// some code
break;
default:
//code displayed when $a does not match any case statements
}
Hope that helps. Also, switch statements execute quite fast, they are basically similar to nested if statements. Thus there is no limit really, however, code optimization is always something you should strive for.

Answer 5

Your switch statement break because your using wrong structure of switch, check complete switch statement reference here
<?php
$i = 1;
switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
default:
echo 'no case match';
break;
}
?>