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