Руководство по PHP
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# Глава 16. Control Structures

Any PHP script is built out of a series of statements. A statement can be an assignment, a function call, a loop, a conditional statement or even a statement that does nothing (an empty statement). Statements usually end with a semicolon. In addition, statements can be grouped into a statement-group by encapsulating a group of statements with curly braces. A statement-group is a statement by itself as well. The various statement types are described in this chapter.

# if

The if construct is one of the most important features of many languages, PHP included. It allows for conditional execution of code fragments. PHP features an if structure that is similar to that of C:

    if (expr)
        statement

As described in the section about expressions, expression is evaluated to its Boolean value. If expression evaluates to `TRUE`, PHP will execute statement, and if it evaluates to `FALSE` - it'll ignore it. More information about what values evaluate to `FALSE` can be found in the 'Converting to boolean' section.

The following example would display `a is bigger than b` if $a is bigger than $b:

`<?php if ($a > $b) echo "a is bigger than b"; ?>`

Often you'd want to have more than one statement to be executed conditionally. Of course, there's no need to wrap each statement with an if clause. Instead, you can group several statements into a statement group. For example, this code would display `a is bigger than b` if $a is bigger than $b, and would then assign the value of $a into $b:

`<?php if ($a > $b) { echo "a is bigger than b"; $b = $a; } ?>`

If statements can be nested indefinitely within other if statements, which provides you with complete flexibility for conditional execution of the various parts of your program.

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