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Control Structures

if
else
elseif
Alternative syntax for control structures
switch
declare
return

if

If allows for conditional execution of code fragments.

<?php
if (expression)
statement
?>


else

Often you'd want to execute a statement if a certain condition is met, and a different statement if the condition is not met. This is what else is for. else extends an if statement to execute a statement in case the expression in the if statement evaluates to FALSE. For example, the following code would display a is bigger than b if $a is bigger than $b, and a is NOT bigger than b otherwise:

<?php
if ($a > $b) {
echo "a is bigger than b";
} else {
echo "a is NOT bigger than b";
}
?>

elseif

elseif, as its name suggests, is a combination of if and else. Like else, it extends an if statement to execute a different statement in case the original if expression evaluates to FALSE. However, unlike else, it will execute that alternative expression only if the elseif conditional expression evaluates to TRUE. For example, the following code would display a is bigger than b, a equal to b or a is smaller than b:

<?php
if ($a > $b) {
echo "a is bigger than b";
} elseif ($a == $b) {
echo "a is equal to b";
} else {
echo "a is smaller than b";
}
?>

There may be several elseifs within the same if statement. The first elseif expression (if any) that evaluates to TRUE would be executed.

Alternative syntax for control structures

PHP offers an alternative syntax for some of its control structures; namely, if, while, for, foreach, and switch. In each case, the basic form of the alternate syntax is to change the opening brace to a colon (:) and the closing brace to endif;, endwhile;, endfor;, endforeach;, or endswitch;, respectively. These alternative syntax are often used to group mutiple statments together.

<?php if ($a == 5): ?>
A is equal to 5
<?php endif; ?>

The alternative syntax applies to else and elseif as well. The following is an if structure with elseif and else in the alternative format:

<?php
if ($a == 5):
echo "a equals 5";
echo "...";
elseif ($a == 6):
echo "a equals 6";
echo "!!!";
else:
echo "a is neither 5 nor 6";
endif;
?>

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.

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;
}
?>

declare

The declare construct is used to set execution directives for a block of code. The syntax of declare is similar to the syntax of other flow control constructs:

declare (directive)
statement

The directive section allows the behavior of the declare block to be set. Currently only one directive is recognized: the ticks directive. (See below for more information on the ticks directive)

The statement part of the declare block will be executed -- how it is executed and what side effects occur during execution may depend on the directive set in the directive block.

The declare construct can also be used in the global scope, affecting all code following it.

<?php
// these are the same:

// you can use this:
declare(ticks=1) {
// entire script here
}

// or you can use this:
declare(ticks=1);
// entire script here
?>

Ticks
A tick is an event that occurs for every N low-level statements executed by the parser within the declare block. The value for N is specified using ticks=N within the declare blocks's directive section.

return

If called from within a function, the return() statement immediately ends execution of the current function, and returns its argument as the value of the function call.

return() will also end the execution of an eval() statement or script file.

If called from the global scope, then execution of the current script file is ended. If the current script file was include()ed or require()ed, then control is passed back to the calling file.

Furthermore, if the current script file was include()ed, then the value given to return() will be returned as the value of the include() call. If return() is called from within the main script file, then script execution ends.


 
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