Data Types for PHP

PHP is a weak type of language, Java, C language, C + + is a strong type of language;

In PHP, when we declare a variable, we do not need to set the data type, but the value to determine the type of the variable ;

Eight Big data types

4 Types of scalar data:

1. Integral type: int

An integer in memory accounts for 4 bytes, no matter how long you keep the data, it takes 4 bytes, an integer type of data, and a range of more than 2 billion;

2. Float Type: float

Single precision: A decimal number after the decimal point, accounting for 4 bytes

Double: there are several decimal places after the decimal point, accounting for 8 bytes

3. Strings string

Definition string: Single quote ' double quotation mark ' delimiter <<<

The difference between single and double quotation marks

• Double quotes inside can parse variables, single quotes will be inside the output intact;

Echo ' $result '; echo "$result";

• Escape character \ will \ Transfer characters after the intact output

Single quotation mark: \ $result

Double quotes: $result

• It is recommended to use single quotes, double quotes to determine whether there are variables, execution speed is slower than single quotes

• Single quotes cannot be nested with single quotes, double quotes cannot be nested double quotes

PHP delimiter <<<

Requirements: In PHP files, you need to output a bit of JavaScript code;

Idea: The browser shows the result of the parsed PHP file, returning a piece of JavaScript code to the browser;

<?php    $str =<<<    <script>           alert (' Welcome to PHP ');     </script>eot;     echo $str;     Var_dump ($STR);  <<< EoT at the back of the letter, indicating the beginning of the string;   EoT; to shelf the end of the string;?>

4. Boolean bool

True False

When converting to a bool value, the case is considered false:

False itself;

Integer value 0;

Floating-point value 0.0;

The empty string and the string "0";

an empty array;

Objects that do not include any member variables;

NULL;

A SimpleXML object without any marks;

Two types of composite data

5. Array arr

$arr =array (1,2,3,4,5);  An array can hold multiple values var_dump ($arr); Echo ' <br/> ';

In PHP, the array () function is used to create arrays;

Indexed array: An array with a numeric index;

$cars =array ("Volvo", "BMW", "ASSB"), or$cars[0]= "Volvo", $cars [1]= "BMW"; $cars [2]= "ASSB"; echo "I like". " $cars [0]. ",". $cars [1]. "and" $cars [2] ".";

Associative array: An array with the specified key;

$aga =array ("Peter" = "The", "ben" = "Notoginseng", "Joe" = "or$age["), "Peter"]= "a", $age [' Ben ']= "Notoginseng"; $age [' Joe ']= ' "Echo" Peter is "$age [Peter]." Years-old. "

Multidimensional array: An array that contains one or more arrays

6. Object Obiect

$db =new mysqli (' localhost ', ' root '); Var_dump ($db); Echo ' <be/> ';

　　

Data Types for PHP