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switch
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 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.
Note that switch/case does loose comparision.
The following two examples are two different ways to write the
same thing, one using a series of if and
elseif statements, and the other using the
switch statement:
Example 7.1. switch structure
<?php
if ($i == 0) {
echo "i equals 0";
} elseif ($i == 1) {
echo "i equals 1";
} elseif ($i == 2) {
echo "i equals 2";
}
switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
}
?>
Example 7.2. switch structure allows usage of strings
<?php
switch ($i) {
case "apple":
echo "i is apple";
break;
case "bar":
echo "i is bar";
break;
case "cake":
echo "i is cake";
break;
}
?>
It is important to understand how the switch
statement is executed in order to avoid mistakes. The
switch statement executes line by line
(actually, statement by statement). In the beginning, no code is
executed. Only when a case statement is found
with a value that matches the value of the
switch expression does PHP begin to execute the
statements. PHP continues to execute the statements until the end
of the switch block, or the first time it sees
a break statement. If you don't write a
break statement at the end of a case's
statement list, PHP will go on executing the statements of the
following case. For example:
<?php
switch ($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 ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
default:
echo "i is not equal to 0, 1 or 2";
}
?>
The case expression may be any expression that
evaluates to a simple type, that is, integer or floating-point
numbers and strings. Arrays or objects cannot be used here unless
they are dereferenced to a simple type.
The alternative syntax for control structures is supported with switches. For more information, see Alternative syntax for control structures.
<?php
switch ($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;
?>