PHP comments definition of data type variables/retrieval/conversion of output types variable, Data Type Variable

PHP comments definition of data type variables/retrieval/conversion of output types variable, Data Type Variable

Annotation method:

1. Single line comment ://

2. Multi-line comment :/**/

Ii. Data Types

1, integer: In a 32-bit operating system, the valid range is-2147483648 ~ + 2147483648;

2. string: string variables are different from character and string variables in other programming languages. In PHP, character variables are used to define characters or strings;

3, boolean (boolean): This is the simplest type, and only two return values (true/false );

4. folat (float, also called double): The valid range of the 32-bit operating system is: 1.7E-308 ~ 1.7E + 308;

There are two composite types:

Array: the array stores multiple values in a variable;

Object: a special data type ------------------------------------------------------------------------------------------------------------------------------------

| Objects must be explicitly declared in PHP.

| First, we must declare the class of the object. A class is a structure that contains attributes and methods.

| Then we define the data type in the object class

Certificate ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Two special types:

NULL (NULL type): indicates that this variable has no value. The only possible value of the NULL type is NULL;

Resource: the source is a special variable that stores a reference to an external resource. resources are created and used by dedicated functions.

3. PHP variable definition

Note:PHP is a weak type language. During definition, PHP automatically determines the type based on the type of the value stored in the variable;

1. Define the value of a as 10: $ a = 10;

2. Define the string: $ a = "abcdef"; or $ a = 'abcdef ';

Note: The difference between single double quotation marks: Double quotation marks can be translated. single quotation marks cannot be translated as strings only;

3. Special definition: $ a >>>

Define the content of a string or HTML code

A; there cannot be any leading space;

A;

4. Data Type acquisition;

Echo gettype ($ );

5. Output of Variables

　1, echo (commonly used)

Echo $ a, "1234"; // multiple strings can be output simultaneously;

2, print

Print $ a; // only one string can be output;

3. Special Output Method

Print_r ([1, 2]); // you can print an array;

For example, the page displays -------- Array ([0] => 1 [1] => 2)

Var_dump ($ B); // all information about the output variable, which is generally used for debugging errors;

6. PHP data type conversion

1,Method 1:

$ A = (string) $ a; // forcibly converts the type of variable a to a string.

2. Method 2:

Settype ($ a, "string"); // forcibly convert the type of variable a to a string.

7. Variable:

$ A = "abc ";

$ Abc = "Zhang ";

Echo $;

Output result: Zhang San