What does 'boolean' variable mean in PHP?

Boolean
For programming languages, if they need to make judgments, they only know true and false, 1 and 0, that is, true and false. Simple judgment.
There are only two Boolean: true and false

For example, if I say 1 is greater than 5, the computer will calculate it by itself. If it is not greater, it will return false, otherwise it will return true. We use this returned true or false to proceed with the next step.

Boolean values ​​are generally used for conditional judgment. It is a name. There are actually two true and false, both of which are constants. Just call it directly.

The difference between empty (NULL) and '' "" (emptystring)
Many people think that these two are the same, but they are actually different.
In the database, it is obvious that empty means it does not exist; and the empty string just means that we think there is nothing in it, but in fact the computer thinks it exists.
For example: For example, two people (J and K) applied for a company together. The company hired K and signed a contract. At the same time, he told J that he was sorry that there is no position for you and will inform you next time.
The K who signed the contract has not yet received the money, you can treat k as an empty string.
And J is just a verbal promise from this company. If there is no contract, you can understand it as empty (NULL)

In PHP, the following data will be considered as Boolean false:
1, false, Including string
2, 0, empty (NULL, case-insensitive), empty array (there is an array but no elements, as if a shell company has no employees), floating point type "0.0"
In a nutshell , except for these, everything else is true~
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string is a "string" or a "character variable"
Generally in the php manual often appears in, for example:
string $k
String variable $k, this variable is required to be a string

The simple meaning of string is: "A string of characters, including Chinese, English, Special symbols and a mixture of numbers are called strings"
For example:

$a='aaa11145ggg';
$b='我也是字符串啊';
$c='2008-8-23';//虽然我是日期，但是我在php里被划到了字符串里去了；但是我的兄弟时间戳是整型

These are all strings
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If you see int $k
, it means: integer $k, which must be a number without a decimal point (it can only be a number, but whether it is positive or negative )
For example:

$a=100;
$b=-100;

These are integer types
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Since there are integers, there must be numbers with small dots. In programming languages ​​(including PHP), it is called "floating point" floor
floor $k;
Requires $k to be floating point
These are floating point types:

$a=0.5;
$b=10.5;
$c=-0.5;

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Array variable: array $k;
The requirement is an array. The array can be automatically generated by the function or defined by ourselves.
Method of custom function: array(), you can check it in the manual
I won’t go into details here, you can read the manual. Arrays have two concepts:
keys Name (equivalent to the serial number in the array, can be a number or a string)
value (equivalent to the specific data corresponding to the variable, can be any data or an array, such an array is called two-dimensional Array,

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