What does && mean in php

In PHP, "&&" means "and" and is a logical operator, which means "logical AND". The result of the operation is a Boolean value; when using "&&" for operation, only When the left and right expressions are TRUE at the same time, the result is TRUE; when either expression of the two expressions is FALSE, the result is FALSE.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

In php, "&&" means "and" and is a logical operator, which means "logical AND".

Logical operators are usually used to combine multiple expressions. The result of a logical operator is a Boolean value, which can only have two results, either true or false.

Logical operators	Examples	When the result is true
&& or and (logical AND)	$m && $n or $m and $n	The result is true when $m and $n are both true, $m and $n The result is false when any one is false

"&&" or "and" logical AND

two left and right expressions When both conditions are TRUE, the result is TRUE; when either expression in the two conditions is FALSE, the result is FALSE. When the condition on the left is FALSE, the condition on the right will be skipped and FALSE will be returned directly.

Logical AND is a kind of short-circuit logic. If the expression on the left is false, the result will be short-circuited and returned directly, and the expression on the right will no longer be evaluated. The operation logic is as follows:

• Step 1: Calculate the value of the first operand (expression on the left).

• Step 2: Detect the value of the first operand. If the value of the first operand can be converted to false (such as null, undefined, NaN, 0, "", false), then the operation ends directly and false is returned.

• Step 3: If the first operand can be converted to true, evaluate the second operand (the expression on the right).

• Step 4: true if the second operand is convertible to true; false if the second operand is convertible to false.

[Example] Assume that people between the ages of 18 and 25 meet the conditions for military recruitment, and Xiao Ming is 21 years old this year. To determine whether Xiao Ming is suitable for military service, the implementation code is as follows:

<?php
header(&#39;content-type:text/html;charset=utf-8&#39;);   
$age = 21;
if($age >= 18 && $age <= 25){
    echo &#39;符合当兵条件！&#39;;
}else{
    echo &#39;不符合当兵条件！&#39;;
}
?>

Extended knowledge:

Logical operators are used to combine the results of logical operations and are a very important set of operations in programming symbol.

Logical operators in PHP are shown in the following table:

Logical operators	Examples	When The result is true
&& or and (logical AND)	$m && $n or $m and $n	When $m and $ The result is true when n are both true, and the result is false when either $m and $n are false
|| or or (logical OR)	$ m || $n or $m or $n	As long as any one of $m and $n is true, the result is true
xor (logical exception Or)	$m xor $n	When $m and $n are one true and one false, the result is true
! (logical negation)	!$m	When $m is false, the result is true

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