Why the same value in php may not be equal to

In the PHP programming language, identical values ​​are considered not equal in some cases. This may be confusing to some novice programmers, since in many other programming languages ​​the same values ​​are often considered equal. In this article, we explore why the same values ​​may not be equal in PHP.

First of all, we need to understand the two types of comparison methods in PHP: value comparison and type comparison. In value comparison, two variables are considered equal when their values ​​are equal. On the other hand, in a type comparison, in addition to having equal values, the two variables must also have the same type.

Let's look at some examples to understand this better. Suppose we have two variables $x and $y, both of which are set to the number 1. In value comparison, it's obvious that they are equal. So, in the following PHP code, the output $x == $y returns true:

$x = 1;
$y = 1;

if ($x == $y) {
    echo "x == y is true";
} else {
    echo "x == y is false";
}

However, in type comparison, the situation may be different. Let's illustrate with an example. Suppose we have a variable $x, which is set to the number 1, and a variable $y, which is set to the string "1". In a type comparison, they are not equal because their types are different. So, in the following PHP code, it will output $x === $y and return false:

$x = 1;
$y = "1";

if ($x === $y) {
    echo "x === y is true";
} else {
    echo "x === y is false";
}

Now, let’s look at some more Complex example. Let's assume there are two variables $a and $b, which are set to the following strings:

$a = "apple";
$b = "apple";

In the first example, we compare the values ​​of the two variables $a and $b. Returns true for the output $a == $b:

if ($a == $b) {
    echo "a == b is true";
} else {
    echo "a == b is false";
}

However, in the next example, we perform a type comparison on the two variables $a and $b. Will output $a === $b Returns false:

if ($a === $b) {
    echo "a === b is true";
} else {
    echo "a === b is false";
}

This is because, although their values ​​are the same, their data types are different. Therefore, they are considered unequal when doing type comparisons.

In PHP, another factor that may cause the same value to be unequal is the automatic conversion of data types. Let's look at an example. Suppose we have a variable $x, which is set to the number 0, and a variable $y, which is set to the string "false". In the code below, we do a "same value not equal" comparison of $x and $y, because in this case, PHP will convert the string "false" into the number 0 for comparison.

$x = 0;
$y = "false";

if ($x == $y) {
    echo "x == y is true";
} else {
    echo "x == y is false";
}

The above code will output $x == $yreturns true, although their data types are different. This is because PHP calculates them to be the same based on their values. However, in a type comparison, $x === $y will return false because their data types are different.

To summarize, although in some cases the same values ​​​​seem to be unequal in PHP programming, it is actually just because PHP has different type comparison methods and automatic type conversion. When writing code, we need to understand these differences and choose the appropriate comparison method according to our needs.

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