PHP we learned together in those years (2)_PHP Tutorial

Now we enter the Linux world and start our PHP coding journey. Various problems will occur during coding, and the time to solve the problems is also the moment when we transform from a novice.
Every programming language will start by practicing variables. PHP is a type of embedded scripting language. Of course, you can also start from the data type of syntax. This section mainly starts with PHP data types and data variables.
Data types of PHP language:
(1) Boolean value, [true, false] Question: There are only two definitions of Boolean value: true, false. PHP defined variables agree to be represented by $ , such as $shop=false;
(2) The integers supported by integers [decimal, octal, hexadecimal] are related to the platform. For PHP5 and previous versions, +2 raised to the 31st power is supported, and PHP6 was introduced 63 times Square integer data. Decimal and hexadecimal are basically converted according to mathematical rules.
(3) Floating-point data, including single-precision floating point [float], double-precision floating point [double], real number [real number], which can contain decimal parts and is used to represent currency, distance, and simple Other representations that cannot be satisfied by integers, such as defining a number $money=1.0093, which defaults to a floating point type value.
(4) Single quote string, that is, use single quotes to enclose the text you want to use. For example: 'I am Siron.'
Q: If I want to write This's book is highly enjoyable. How should I write it?
Note on the simultaneous use of single and double quotes in PHP:
Double quote fields will be interpreted by the compiler and then output through HTML code.
Single quote fields will not be interpreted by the compiler and will be output directly.
For example:

(5) Double quotation mark string, that is, use double quotation marks to enclose the text you want to use, but it is more complicated. Variable substitution can be used within double quotes. For example: "I am Siron."
(6) Array type. Arrays can exist in the form of key-value pairs and support multi-dimensional arrays. Brief definition example


(7) The object type is a conforming data type, which will be introduced in detail later in object-oriented programming.
$
blengder =new Application;
(8) resource type
$file=fopen("1.txt",r)//This is the resource type
(9) PHP Is it a weakly typed language? Is it possible to force type conversion?
Regarding PHP’s forced type conversion (that is, converting one data type to another type), it can be achieved by adding the forced data type in front of the variable. But please pay attention to the conversion process , when high-precision floating point numbers are converted to low-precision values, the data of the variable is lost, so it must be used with caution. The types of forced conversion are (bool) (array) (int) (integer) (object) (real) (double) (float) ( string). PHP type definitions are very loose, so sometimes the reference variable is automatically converted to the appropriate type based on the environment system in which it is located.

(10) What built-in functions are used related to types?
PHP built-in uses the gettype() function to return the variable type specified by Var, and uses settype() to convert var to the type specified by Type. That is: gettype() This function is used to get the type of the variable. The returned type string may be one of the following strings: integer, double, string, array, object, unknown type. Syntax: string gettype(mixed var);
settype() This function is used to configure or convert variable types. Returns true value on success, false value otherwise. The parameter var is the original variable name, and the parameter type is one of the following types: integer, double, string, array and object. Syntax: int settype(string var, string type);