php--switch statement

A switch statement is similar to a series of if statements with the same expression. There are many situations where you need to compare the same variable (or expression) with many different values ​​and execute different code depending on which value it equals. This is exactly what the switch statement is for.

Note: Note that unlike other languages, the continue statement acts similarly to break when applied to switch. If you have a switch in a loop and want to continue to the next iteration in the outer loop, use continue 2.

Note:

Note that switch/case does a loose comparison.

The following two examples use two different methods to achieve the same thing, one using a series of if and elseif statements, the other using a switch statement:

Example #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 #2 switch structure can use characters String

<?php
switch ($i) {
case "apple":
    echo "i is apple";
    break;
case "bar":
    echo "i is bar";
    break;
case "cake":
    echo "i is cake";
    break;
}
?>

To avoid errors, it is important to understand how switch is executed. The switch statements are executed line by line (actually statement by statement). Initially no code is executed. Only when the value in a case statement matches the value of the switch expression will PHP start executing the statement until the end of the switch block or until the first break statement is encountered. If break is not written at the end of the statement segment of the case, PHP will continue to execute the statement segment in the next case. For example:

<?php
switch ($i) {
    case 0:
        echo "i equals 0";
    case 1:
        echo "i equals 1";
    case 2:
        echo "i equals 2";
}
?>

If $i equals 0, PHP will execute all echo statements! If $i equals 1, PHP will execute the next two echo statements. Only if $i equals 2 will you get the "expected" result - just "i equals 2". Therefore, it is important not to forget break statements (even when you deliberately want to avoid providing them in some cases).

The condition in the switch statement is only evaluated once and compared with each case statement. The condition is evaluated again in the elseif statement. If the condition is more complex than a simple comparison or is in a loop many times, it may be faster to use a switch statement.

The statements in a case can also be empty, which just transfers control to the statements in 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 of case is default. It matches any case that does not match any other case. 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";
}
?>

case expression can be any expression that evaluates to a simple type, i.e. an integer or floating point number as well as a string. Arrays or objects cannot be used unless they are dereferenced to simple types.

switch supports flow control with alternative syntax.

<?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;
?>

allows the use of semicolons instead of colons after case statements, for example:

<?php
switch($beer)
{
    case &#39;tuborg&#39;;
    case &#39;carlsberg&#39;;
    case &#39;heineken&#39;;
        echo &#39;Good choice&#39;;
    break;
    default;
        echo &#39;Please make a new selection...&#39;;
    break;
}
?>