PHP Introductory Training tutorial PHP variables and constants

　First, the basic grammatical format of PHP5.4

1. PHP Separator

$php =true; Semicolon concluding sentence

if ($php) {

echo "true"; Semicolon concluding sentence

}//Curly brace concluding sentence

?>

　2. PHP comments and syntax identifiers (

）

(1), single line comment//note from C + + Note

(2), multiline comment/* */Note from C language

3, the function of the use of the format

(1) Return value function name ()

(2) Return value function name (parameter, parameter)

(3) Function name (parameter, parameter, return variable)

(4) Return value function name (...) Usage of general characters//PHP5.4

The data types of variables and variables of PHP5.4

A variable is preceded by a dollar sign "$", and "$" is followed by an identifier. The identity string consists of letters, numbers, underscores, and cannot begin with a number.

$php =true; Semicolon concluding sentence

if ($php) {

echo "true"; Semicolon concluding sentence

}//Curly brace concluding sentence

$url = "Blog.csdn.net/dawanganban"; Defining variables

echo $url;

Unset ($url); Delete a variable URL

echo $url;

?>

How variables are named

(1) Direct connection between words

$titlekeyword

(2) Connect the words with an underscore

$title _keyword

(3) initial capital (hump) between words

$titleKeyword

The data types of PHP are as follows:

(1) String: The contents of single quotation marks (simple quotation marks) or double quotation marks (functional quotes)

(2) Integral type (integer): -2^32 < n < 2^32-1

(3) floating-point character (float or double) 1.8E+308 (1.8 x 10^308)

(4) Boolean (Boolean) True or False

(5) Arrays (array)

(6) Objects (object)

Class person{

Public $userName = "Sunshine cockroach";

Public Function getmsg () {

echo "Name:". $this->username;

}

}

$p =new person ();

$p->getmsg ();

?>

(7) resource type (resouce) system data Resources

A resource is a special type of data that cannot be directly derived and needs to be accessed through a specialized function:

Database access must be implemented through the MySQL function library, the MYSQLI function library, or the PDO function library.

File access must be implemented through the FileSystem function library.

Directory operations must be implemented through the Directory function library.

Image operations must be implemented through the GD function library.

(8) null value (NULL)

System constants and custom constants for PHP5.4

Constants cannot change data during program execution, and the scope of constants is global. The name of a constant is similar to a variable, except that it does not have a "$" symbol. A valid constant starts with a letter or an underscore, and generally in PHP, the constants are uppercase and are divided into system constants and custom constants.

Example System constants:

__file__ default constant, refers to the PHP program file name and path

__line__ default constant, which is the number of lines in a PHP program

Name of the __class__ class

In PHP, you define a constant by using the Define () function, which has the following syntax format:

BOOL Define (String $name, mixed $value [, BOOL case_$insensitive])

Name: Names of constants

Value: Values of constants

Insensitive: Specifies whether the name of the constant is case sensitive. True is not case-sensitive, and if set to false is case-sensitive, the default value is False.

Define ("COLOR", "Red"); Defines a constant color with a value of red

echo COLOR. "

"; The value of the output constant color

Variable variable

$a = "B"

$ $a = "123"//variable variable

Echo $b;

Output Result: 123

To output a variable in a string, use double quotation marks

$a = 50;

Echo ' I have a $ A yuan '; single quotation mark

echo "I have a $ A yuan";

You can execute more of the signifier characters in double quotes, such as \ t \ r

Judging data types

$a = "5";

$a =-5;

Var_dump ($a);

PHP Introductory Training tutorial PHP variables and constants