PHP Lesson 3 Basic Data Types of PHP

PHP Lesson 3 Basic Data Types of PHP

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

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

 ";print_r ($arr);echo "

";?>


Array value:

Add an array:

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

 Say ();?>

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

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: $ Conn = mysql_connect ("localhost", "root", "1234 ");
Var_dump (is_resource ($ conn ));
?>

4. Automatic type conversion
1. integer-> string

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)

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