The various usages of the PHP switch method

The

is only so called "advanced" usage because I have not mastered the most basic usage of the switch, so, the following is actually the basic usage of it! The
 
Switch statement is similar to a series of IF statements that have the same expression. There are many situations where you need to compare the same variable (or expression) with a number of different values and execute different code based on which value it equals. This is the purpose of the switch statement.
Note: Note that unlike other languages, a continue statement acts on a switch similar to a break. If you have a switch in the loop and want to continue the next cycle in the outer loop, use continue 2.
The following two examples use two different methods for implementing the same thing, one with a series of if statements and the other with a switch statement:
Example #1 Switch structure

The code is as follows	Copy Code
<?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 be used as a string

The code is as follows	Copy Code
<?php Switch ($i) { Case "Apple": echo "I is Apple"; Break Case "Bar": echo "I is bar"; Break Case "Cake": echo "I is cake"; Break } ?>

Key point: (This is the place that I have not mastered before!) ）
To avoid errors, it is important to understand how the switch is performed. The switch statement executes one line at a line (actually a statement-taking statement). No code is executed at the beginning. PHP begins executing a statement only if the value in one case statement matches the value of the switch expression until the end of the switch's program segment (such as a return statement) or when the first break statement is encountered. If you do not write a break at the end of the statement section of the case, PHP will continue to execute the statement section in the next box. For example:

The code is as follows	Copy Code
<?php Switch ($i) { Case 0: echo "I equals 0"; Case 1: echo "I equals 1"; Case 2: echo "I equals 2"; } ?>

Special Note: here if $i equals 3,php will not execute any ECHO statement! However, if $i equals 0,php will execute all the echo statements! If $i equals 1,php, the following two echo statements are executed. Only when the $i equals 2 o'clock will the result of "expected" be given--only "I equals 2" is displayed. So, don't forget that break statements are important (even if you deliberately avoid providing them in some cases).

[Efficiency] The condition in the switch statement is only one time and is used to compare with each case statement. The condition is evaluated again in the ElseIf statement. If the condition is more complex than a simple comparison or in a loop of many times, it may be quicker to use a switch statement.
The statement in a case can also be empty, which simply transfers control to the statement in the next box.

The code is as follows	Copy Code
<?php Switch ($i) { Case 0: Case 1: Case 2: echo "I am less than 3 but not negative"; Break Case 3: echo "I is 3"; } ?>

The exception to a case is default. It matches anything that does not match any other case. For example:

The code is as follows	Copy Code
<?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 am not equal to 0, 1 or 2"; } ?>

A case expression can be any expression that is evaluated as a simple type, that is, an integer or floating-point number, and a string. You cannot use arrays or objects unless they are dereference as simple types.

"Combat" according to the above knowledge point, write such a function: Calculate the capacity value actually represents the number of bytes

code is as follows

copy code

<?php /**  * return bytes  *  * @param string $val such as 4 00M  */ Function return_bytes ($val = ') {   $val = Trim ($val);   $last = Strtolower ($val {strlen ($val)-1});  switch ($last)  {   case ' G ':     $val *= 1024;    Case ' m ':     $val *= 1024   case ' k ':     $val *= 1024;  }< /p>  return $val; } $memorylimit = ini_get (' Memory_limit '); Echo $memorylimit, ' <br/> '; Echo return_bytes ($memorylimit); Output: 400M 419430400

Special Note: $val = 400M, case ' m ' is hit, its $val *= 1024; is executed, but because there is no break language, it will continue to hit case ' K ' and execute its $val *= 1024; statement, so, overall equivalent to the execution 400 * 1024 * 1024.