Constants basics PHP basic learning the use of variables

Copy code The code is as follows:

//Quote
$
echo $$three."
";//Output "one"
echo $$$three."
";//Output "######"
//There are 8 types in php
//4 kinds of scalars: int integer
// bool boolean
// float, double, real
/ / string
//2 composite types: array
// object
//2 special types: resource type resource
// empty type null
//declaration of integer
$int=10; //declaration of decimal
$ int=045;//Octal declaration
$int=0xff;//Hexadecimal declaration
$float=3.14E+5;//Scientific notation
$float=3.14E-5;
//All of them In the case of false
$bool=false;
$bool=0;
$bool=0.000;
$bool=null;
$bool="";
$bool=" ";
$bool="0";
$bool=array();
//Declaration of strings
//1. Both single quotes and double quotes can declare strings
//2. There is no length limit for the declared strings
//3. In double quotes In a string, variables can be parsed directly, or escape characters can be used directly (the single quote itself can be escaped, or the escape character "" can be escaped)
//4. In a string with single quotes, it is not possible Directly parse variables, and escape characters cannot be used
//5. Double quotes cannot be used within double quotes, and single quotes cannot be used within single quotes
//6. It is best to use single quotes,
$str= 'aaaaa';
$str="aaaa";
//Delimiter declares a string, a large number of strings
//test is a customized string, there cannot be any characters after it, and spaces are not allowed either
// It must also end with the custom string test. There cannot be any characters before the end.
$str=this write content...
test;
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The above introduces the use of variables in Constants basic PHP basic learning, including the basic aspects of Constants. I hope it will be helpful to friends who are interested in PHP tutorials.