PHP variables and constants

This section describes

(1) FEATURES of PHP files

(2) PHP variables

(3) PHP constant

1. PHP file features

  • The suffix for the PHP file is.php
  • PHP scripts to<? phpAt the beginning,? >Ending, in which? >The ending character can be omitted
  • PHP statements start with semicolons;The end of the
  • PHP files usually contain HTML tags and some PHP script code; PHP can be placed anywhere in the document
  • The server wax interface file is typically pure PHP script code
  • ** Note: ** files containing PHP scripts must use PHP as the file name, otherwise the PHP script will not parse
  • Example 1:

    • Create the file example.html

    • HTML, CSS, related grammar reference: www.w3school.com.cn/h.asp (there is no need to do)

    • <! DOCTYPE html> <html> <head> <meta charset ="UTF-8"> < title > my homepage < / title > < / head > < body > < h2 > this is my page < / h2 > < hr > <? phpecho "PHP code"; ? > </body> </html>Copy the code

    • Saved to run a web root directory, use the browser to visit: http://localhost:8888/example.html, you can see the results as follows, the content of the PHP does not show:

    • Change the file name to example. PHP and refresh the page.

2. PHP comments

(1) Single-line comments

  • // This is a one-line comment
  • # This is a one-line comment

(2) Multi-line comments

  • /* This is a multi-line comment that can span multiple lines */Copy the code

3. PHP echo statement

  • PHP often uses echo to enter the value of a string or variable
  • Echo is divided into no parentheses and with parentheses
  • Echo prints a string that can contain HTML tags
  • Example 2:
    • Create the file echo.php
    • <? phpecho "Echo example < br >" ;

$a= 2020;echo $a ;
echo "<br>" ;
echo ($a) ;

?>
Copy the code

4. PHP variables

(1) PHP variable rules

  • Variables begin with a $sign, followed by the name of the variable
  • Variable names must begin with a letter or underscore
  • Variable names cannot start with a number
  • Variable names can contain only alphanumeric characters and underscores (A-z, 0-9, and _)
  • Variable names are case-sensitive (Y is two different variables.)

(2) PHP variable types

  • PHP has no command to create variables
  • Variables are created the first time they are assigned a value
  • PHP is a loosely typed language, so you don’t have to tell variables their data types
  • PHP automatically converts a variable to the correct data type based on its value

(3) PHP prints variable types

  • Generally used for checking and debugging
  • To view the value and type of an expressionvar_dump()
  • To get the type of a variable or expressiongettype()
  • is_typeFunction to determine whether a variable is of a type, such as is_int, is_double, is_string, etc

5. PHP constant

  • Constants are like variables, but they cannot be changed or undone once defined
  • PHP USESdefine()The function defines a constant, which takes three arguments:
    • (1) The first argument defines the name of the constant
    • (2) The second argument defines the value of the constant
    • (3) The optional third argument specifies whether the constant name is case-sensitive. The default is false(case sensitive). Such as:
      • define("LOGO","Welcome to Bernadette!" ,true);
      • echo LOGO;
      • echo logo;
      • Print all ofWelcome to Bernadette!