Detailed explanation of PHP expression concepts and examples

What is a php expression?

Expressions are the basic elements that make up the PHP programming language, and they are also the most important component of PHP. Just like building a house, a foundation is indispensable. In PHP, almost everything written is an expression. Mode.

The most basic forms of expressions are constants and variables. For example, $a=10 means assigning the value 10 to the variable $a.

Look at a simple expression example:

$a>$b

The above is an expression. When the value of $a is greater than $b, the expression value is TRUE, otherwise it is FALSE.

Expressions are implemented through specific codes. We often use an expression to determine a value (including specific numerical values ​​and Boolean values) to do the next step. Just like the example below.

<?php
if ($a < $b) {
    echo "a< b";
}else{
    echo "a> b";
}
?>

In the above example, we used the if judgment statement. The judgment condition is the "$a < $b" expression in the brackets. If $a < $b is true, "a< b" will be output ", otherwise "a> b" will be output.

This is just a simple expression. In actual development, it will be much more complicated.

In addition to the simple expression above, there is also a continuous assignment expression, think of the following:

$b=$a=100

In PHP, the order of assignment operations is From right to left, so variables $b and $a are assigned the value 100.

In PHP, we use semicolon ";" to distinguish expressions and statements. Expressions can be enclosed in parentheses, as in the example above. You can simply understand it as: an expression plus a semicolon constitutes a PHP statement.

Something to note here is that when we write the program, do not miss the ";" semicolon. Missing the semicolon is a common mistake made by many PHP novices.

Expressions can do many things, such as calling an array, creating a class, assigning values ​​to variables, etc.

PHP expression usage example:

<?php
$a=10;
$b=20;

if ($a < $b) {
    echo "a< b";
}else{
    echo "a> b";
}
?>

Code running result:

In the above example, $ a=10, $b=20 are expressions, and "$a

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