PHP Lesson 3: Basic Data Types of PHP, and php Data Types

PHP Lesson 3: Basic Data Types of PHP, and php Data Types

Learning outline:

1. php seven variable types

2. Differences between isset and empty Functions
3. Type Test
4. Automatic type conversion

5. Forced type conversion

Note:

1. The call method in the object is called through the variable-> method name. $ user1 = new per (); $ user1-> say ();
2. Change the page encoding:
Header ("content-type: text/html; charset = gbk ");
3. the header information cannot be output.

1. php eight variable types
Integer
Floating Point Type
Character Type
Boolean
// The above four types are scalar types

Array
Object
// The above two types are composite types

Resources
Null type
// The above two types are special



Integer
$ A = 10;
Floating Point Type
$ A = 10.3;
Character Type
$ A = "Hello World ";
Use. To link strings

<?php$hello = "Hello";echo $hello."  World";?>

Boolean
$ A = true;
Boolean types are generally obtained by comparison operations,> <>==! ===! =
When echo print_r is used to output a boolean type, true is changed to 1, and false is null.
$ A = true;
Var_dump ($ );
Array
// Definition: when multiple values are assigned to a variable

<?php    $arr=array("hello","world","junzaivip",88,true);echo "<pre>";print_r ($arr);echo "</pre>";?>

Array value:

<?php    $arr=array("hello","world","junzaivip",88,true); echo $arr[1];?>

Add an array:

<?php    $arr=array("hello","world","junzaivip",88,true);    $arr[] = "d";    print_r($arr);?>

Object Type
// An object consists of features and functions, attributes, and methods.

<? Phpheader ("content-type: text/html; charset = gbk"); class per {function say () {echo "I'm talking";} function eat () {echo "I'm eating" ;}function sleep () {echo "I'm sleeping" ;}function run () {echo "I'm walking ";}} $ user1 = new per (); $ user1-> say ();?>

Resources
Null type
$ A = null;
Database-based linked resources and operation tables:

<? Php // header ("content-type: text/html; charset = UTF-8"); $ conn = mysql_connect ("localhost", "root", "1234 "); mysql_select_db ("test"); // select the database mysql_query ("set names utf8"); // set the database encoding to utf8 $ SQL = "select * from user "; // SQL statement // Execute SQL statement $ rst = mysql_query ($ SQL); // extract data while ($ row = mysql_fetch_assoc ($ rst )) {echo "







2. Differences between isset and empty Functions

Whether the isset variable exists and does not exist:

1) No definition

2) null



Whether or not the empty variable is empty:

1) 0

2 )""

3) "0"

4) false

5) array ()

6) null

7) No definition

3. Type Test

Var_dump ();

1. Integer is_int ();

2. Float is_float ();





Database Connection: <? Php

$ Conn = mysql_connect ("localhost", "root", "1234 ");

Var_dump (is_resource ($ conn ));

?>



4. Automatic type conversion

1. integer-> string


<?php   $num=1243;    echo $num."abd";?>



2. String-> integer

$ Num = "1243alj ";

// The string is automatically converted to an integer.

Echo $ num + 1;



3. Other types-> Boolean Type

1) 0

2 )""

3) "0"

4) false

5) array ()

6) null

7) No definition

// The Boolean Type above is false.







5. Forced type conversion

(Int) $ num integer

(Float) $ num floating point type

(String) $ num String

(Bool) $ num Boolean



Use to delete variables:

$ Num = "user ";

Unset ($ num );

Var_dump (isset ($ num ));



Single double quotation marks of a string:

1. If no variable exists in the string, use single quotation marks.

2. If there is a variable, use double quotation marks (single quotation marks can also be used, but must be linked)


<? Php // $ str = 'hello'; // $ str2 = 'World'; // echo $ str. $ str2; $ name = 'lei shun'; echo "I am {$ name}, I want to sleep for a while"; echo 'I am '. $ name. ', I want to sleep for a while'; echo "I am ". $ name. ", I want to go to bed for a while"; // if there is no variable in the string, single quotation marks are used. If there is a variable, double quotation marks are used (single quotation marks can also be used, but must be used. )?>





Constant definition:

// Same as the variable, but cannot be modified once defined

Define ("HOST", "localhost ");

Define ("USER", "root ");

Define ("PASS", "123 ");

Define ("DBNAME", "test ");



// For example, the database configuration file must use constants and cannot be modified later.



Constant output:

Echo HOST;

Constants cannot be placed in double quotation marks.

Echo "my host is". HOST;





Operator






What are the main data types of PHP?
PHP supports eight basic data types.
Four scalar types:
Boolean (boolean)
Integer)
Float (float, also called double)
String (string)
Two composite types:
Array)
Object)
There are two special types:
Resource)
NULL)

Php Data Type?
PHP is a weak language, and variables are of no type and are automatically processed by the compiling environment.
To avoid errors, we recommend that you initialize the variables.
For example, $ var = ''; is the character $ var = 0; is the number $ var = array () is the array