The switch statement is similar to a series of
IF statements on the same expression. In many occasions, you may
want to compare the same variable (or expression) with many
different values, and execute a different piece of code depending
on which value it equals to. This is exactly what the
switch statement is for.
Note:
Note that unlike some other languages, the
continue statement
applies to switch and acts similar to break. If you
have a switch inside a loop and wish to continue to the next iteration of
the outer loop, use continue 2.
In the following example, each code block is equivalent.
One uses a series of if and
elseif statements, and the other a
switch statement. In each case, the output is the same.
Example #1 switch structure
<?php // This switch statement:
switch ($i) { case 0: echo "i equals 0"; break; case 1: echo "i equals 1"; break; case 2: echo "i equals 2"; break; }
// Is equivalent to:
if ($i == 0) { echo "i equals 0"; } elseif ($i == 1) { echo "i equals 1"; } elseif ($i == 2) { echo "i equals 2"; } ?>
It is important to understand how the switch
statement is executed in order to avoid mistakes. The
switch statement executes line by line
(actually, statement by statement). In the beginning, no code is
executed. Only when a case statement is found
whose expression evaluates to a value that matches the value of the
switch expression does PHP begin to execute the
statements. PHP continues to execute the statements until the end
of the switch block, or the first time it sees
a break statement. If you don't write a
break statement at the end of a case's
statement list, PHP will go on executing the statements of the
following case. For example:
<?php switch ($i) { case 0: echo "i equals 0"; case 1: echo "i equals 1"; case 2: echo "i equals 2"; } ?>
Here, if $i is equal to 0, PHP would execute all of the echo
statements! If $i is equal to 1, PHP would execute the last two
echo statements. You would get the expected behavior ('i equals 2'
would be displayed) only if $i is equal to 2. Thus,
it is important not to forget break statements
(even though you may want to avoid supplying them on purpose under
certain circumstances).
In a switch statement, the condition is
evaluated only once and the result is compared to each
case statement. In an elseif
statement, the condition is evaluated again. If your condition is
more complicated than a simple compare and/or is in a tight loop,
a switch may be faster.
The statement list for a case can also be empty, which simply
passes control into the statement list for the next case.
<?php switch ($i) { case 0: case 1: case 2: echo "i is less than 3 but not negative"; break; case 3: echo "i is 3"; } ?>
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"; } ?>
Note:
Multiple default cases will raise a
E_COMPILE_ERROR error.
Note:
Technically the default case may be listed
in any order. It will only be used if no other case matches.
However, by convention it is best to place it at the end as the
last branch.
If no case branch matches, and there is no default
branch, then no code will be executed, just as if no if statement was true.
A case value may be given as an expression. However, that expression will be
evaluated on its own and then loosely compared with the switch value. That means
it cannot be used for complex evaluations of the switch value. For example:
<?php $target = 1; $start = 3;
switch ($target) { case $start - 1: print "A"; break; case $start - 2: print "B"; break; case $start - 3: print "C"; break; case $start - 4: print "D"; break; }
// Prints "B" ?>
For more complex comparisons, the value true may be used as the switch value.
Or, alternatively, if-else blocks instead of switch.
<?php $offset = 1; $start = 3;
switch (true) { case $start - $offset === 1: print "A"; break; case $start - $offset === 2: print "B"; break; case $start - $offset === 3: print "C"; break; case $start - $offset === 4: print "D"; break; }
<?php switch ($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"; endswitch; ?>
It's possible to use a semicolon instead of a colon after a case like:
<?php switch($beer) { case 'tuborg'; case 'carlsberg'; case 'stella'; case 'heineken'; echo 'Good choice'; break; default; echo 'Please make a new selection...'; break; } ?>
This is listed in the documentation above, but it's a bit tucked away between the paragraphs. The difference between a series of if statements and the switch statement is that the expression you're comparing with, is evaluated only once in a switch statement. I think this fact needs a little bit more attention, so here's an example:
switch(++$a) { case 3: echo 3; break; case 2: echo 2; break; case 1: echo 1; break; default: echo "No match!"; break; }
// Outputs: 1 ?>
It is therefore perfectly safe to do:
<?php switch(winNobelPrizeStartingFromBirth()) { case "peace": echo "You won the Nobel Peace Prize!"; break; case "physics": echo "You won the Nobel Prize in Physics!"; break; case "chemistry": echo "You won the Nobel Prize in Chemistry!"; break; case "medicine": echo "You won the Nobel Prize in Medicine!"; break; case "literature": echo "You won the Nobel Prize in Literature!"; break; default: echo "You bought a rusty iron medal from a shady guy who insists it's a Nobel Prize..."; break; } ?>
without having to worry about the function being re-evaluated for every case. There's no need to preemptively save the result in a variable either.
Although noted elsewhere, still worth noting is how loose comparison in switch-case was also affected by the change in string to number comparison. Prior PHP8, strings were converted to int before comparison. The reverse is now true which can cause issues for logic that relied on this behavior.
The default case appears to always be evaluated last. If break is excluded from the default case, then the proceeding cases will be reevaluated. This behavior appears to be undocumented.
<?php
$kinds = ['moo', 'kind1', 'kind2'];
foreach ($kinds as $kind) { switch($kind) { default: // The kind wasn't valid, set it to the default $kind = 'kind1'; var_dump('default');