What is the meaning of '==' symbol in php

In PHP, the "==" symbol is a comparison operator that can compare whether two operands are equal. The syntax is "operand 1 == operand 2". The "==" operator compares and tests whether the variable on the left (expression or constant) has the same value as the variable on the right (expression or constant); it only compares the values ​​of the variables, not the data types. If the two values ​​are the same, it returns a true value; if the two values ​​are not the same, it returns a false value.

The operating environment of this tutorial: windows7 system, PHP8 version, DELL G3 computer

In php, the "==" symbol Is a comparison operator that can compare whether two operands are equal.

Equality (==) operator

The equation (==) operator compares and tests the left Whether a variable (expression or constant) has the same value as the variable (expression or constant) to the right; the comparison performed by this operator is loose.

If the two values ​​​​are the same (it only compares the value of the variable, not the data type), it returns a true value; if the two values ​​​​are not the same, it returns a false value.

Note: The equality (==) operator and the assignment (=) operator are different. The assignment (=) operator changes the variable on the left, assigning the variable on the right to the variable on the left, while the equality (==) operator tests for equality and returns true or false depending on the comparison.

<?php 
header("content-type:text/html;charset=utf-8");  
// 给变量赋整数值
$x = 999; 
echo &#39;$x=&#39;.$x."<br>"; 
// 给变量赋字符串值
$y = &#39;999&#39;; 
echo &#39;$y=&#39;.$y."<br>"; 
//比较$x 和$y 
if ($x == $y) 
    echo &#39;$x和$y的值相等&#39;; 
else
    echo &#39;$x和$y的值不相等&#39;; 
?>

In the above example, because the equality (==) operator only compares the values ​​of variables, the values ​​of $x and $y are equal, so directly The statement in the if is executed, and the else statement is not executed.

Extended knowledge: Identity (===) operator

If you want to compare whether the values ​​are equal and also want to compare data To determine whether they are equal, you need to use the "===" operator.

The identity (===) operator performs a strict comparison between given variables or values; it compares and sees if two variables (expressions or constants) have equal values ​​and have the same data type , i.e. both are strings or both are integers, etc.

This operator returns true if two variables (expressions or constants) contain the same value and the same data type, otherwise it returns false.

<?php 
header("content-type:text/html;charset=utf-8");  
// 给变量赋整数值
$x = 999; 
echo &#39;$x=&#39;.$x."<br>"; 
// 给变量赋字符串值
$y = &#39;999&#39;; 
echo &#39;$y=&#39;.$y."<br>"; 
//比较$x 和$y 
if ($x === $y) 
    echo &#39;$x和$y相等&#39;; 
else
    echo &#39;$x和$y不相等&#39;; 
?>

In the above example, the values ​​of $x and $y are equal but the data types are different, so false is returned and the else part is executed.

PHP Comparison Operators

##$a $b is not equal to is the same as !=, if $a is after type conversion The value of is not equal to the value of $b, then TRUE is returned, otherwise FALSE$a !== $bis not equalIf $ If the value of a is not equal to the value of $b, or the types of their values ​​are different, TRUE is returned, otherwise FALSE is returned $a 小与If the value of $a is less than the value of $b, return TRUE, otherwise return FALSE##$a > $b##$a is less than or equal toIf the value of $a is less than or equal to the value of $b, return TRUE, otherwise return FALSEGreater than or equalSpaceship operator (combined comparison operator) NULL merge operator Recommended study: "PHP Video Tutorial"

Example	Name	Description
$a == $b	is equal to	If the values ​​​​of $a and $b are equal after type conversion, TRUE is returned, otherwise FALSE is returned
$a === $b	Congruent	Returns TRUE if $a and $b are not only equal in value, but also have equal types of their values, Otherwise return FALSE
$a != $b	is not equal to	If the value of $a is not equal to the value of $b after type conversion, then Returns TRUE, otherwise returns FALSE
is greater than	If the value of $a is greater than the value of $b, return TRUE, otherwise return FALSE
		##$a >= $b
If the value of $a is greater than or equal to the value of $b, return TRUE, otherwise return FALSE		$a $b
When $a is less than, equal to, or greater than $b, return an integer value less than, equal to, or greater than 0 respectively. PHP7 starts to provide.		$a ?? $b ?? $c
The first one from left to right exists and Operands that are not NULL. If neither is defined and is not NULL, NULL is returned. Available starting with PHP7.

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