PHP Lesson 3 Basic Data Types of PHP_PHP Tutorial

PHP Lesson 3 Basic Data Types of PHP

Learning Outline:

1.php seven variable types

2. The difference between isset and empty functions
3.Type testing
4. Automatic conversion of types

5. Type casting

Note:

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

1.php eight variable types
Integer
Floating point
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 types



Integer
$a=10;
Floating point
$a=10.3;
Character type
$a="Hello World";
String links use . to link

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

Boolean
$a=true;
Boolean types are generally obtained by comparison operations, > < >= <= == != === !==<= == != === !==
When using echo print_r to output a Boolean type, true will become 1 and false will become empty
$a=true;
var_dump($a);
Array
//Definition: When assigning multiple values ​​to a variable

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

"; ?>


Array value:

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

Array addition:

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

Object type
//Object consists of two parts: characteristics and functions, properties and methods

<?php
	header ("content-type:text/html;charset=gbk");
   class per{
   	   function say(){
   	   	   echo "我正在说话";
   	   	   
   	   	   
   	   }
   	   
   	   function eat(){
   	   	   echo "我正在吃饭";
   	   }
   	   
   	   function sleep(){
   	   	   echo "我正在睡觉";
   	   }
   	   
   	   function run(){
   	   	   echo "我正在走路";
   	   }
   	   
   }
   
   $user1 = new per();
   $user1->say();
   
?>

Resources
null type
$a=null;
Based on database link resources, operation table:

<?php
 //header("content-type:text/html;charset=utf-8");
$conn=mysql_connect("localhost","root","1234");


mysql_select_db("test");//选择数据库
	mysql_query("set names utf8");//设置数据库编码为utf8
$sql="select * from user";//sql语句


//执行sql语句
$rst=mysql_query($sql);


//拿出数据
while($row=mysql_fetch_assoc($rst)){
	echo "<h1> ID:{$row[&#39;id&#39;]}</h1>";
	echo "<h1> NAME:{$row[&#39;name&#39;]}</h1>";
	
	
}




?>	

2. The difference between isset and empty functions
Whether the isset variable exists, if it does not exist:
1) No definition
2)null

empty whether the variable is empty, if it is empty:
1)0
2)""
3)"0"
4)false
5)array()
6)null
7) No definition
3.Type testing
var_dump();
1. Integer type is_int();
2. Floating point type is_float();


Database connection: $conn = mysql_connect("localhost","root","1234");
var_dump(is_resource($conn));
?>

4. Automatic conversion of types
1. Integer->String

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

2. String->Integer
$num="1243alj";
//String is automatically converted to integer
echo $num+1;

3. Other types->Boolean type
1)0
2)""
3)"0"
4)false
5)array()
6)null
7) No definition
//The above conversion to Boolean type is all false



5.Type coercion
(int)$num integer
(float)$num floating point type
(String)$num string
(bool)$num Boolean

To delete a variable use:
$num="user";
unset($num);
var_dump(isset($num));

Single and double quotes for strings:
1. If there are no variables in the string, use single quotes
2. If there are variables, use double quotes (single quotes can also be used, but you need to use . to link)

<?php
        // $str=&#39;Hello&#39;;
        //	$str2=&#39;World&#39;;
        //	echo $str.$str2;
        
        $name=&#39;小磊顺&#39;;
        echo "我是{$name},我想睡一会";
        
        echo &#39;我是&#39;.$name.&#39;,我想睡一会&#39;;
        echo "我是".$name.",我想睡一会";
        
        //字符串中没有变量,就用单引号,如果有变量就用双引号(单引号也可以使用,但是需要用.来链接)
        ?>

Definition of constant:
//Same as a variable, but once defined it cannot be modified
define("HOST","localhost");
define("USER","root");
define("PASS","123");
define("DBNAME","test");

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

Constant output:
echo HOST;
Constants cannot be placed in double quotes
echo "my host is".HOST;


Operator

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