PHPMYSQL basic tutorial _ MySQL

PHPMYSQL basic tutorial 1. three methods of annotation

① # Comment The shell style here

② // Note the c ++ style here

③/* Comments */c-style multi-line comments should not be placed in one line (single-line comments should be used //) to prevent unnecessary errors

2. variables

① The variable starts with $

② The variable name is composed of strings, underscores, and numbers.

③ The variable name must start with a string or underline and cannot start with a number.

④ Variable names are case sensitive. $ name and $ Name are not variables.

⑤ The variable can be assigned a value using =.

3. variables in PHP 8

Four scalar types: Boolean (true and false), integer, floating point, string

Two non-standard values: Array and object

Resources

Null does not have any special type of value

4. echo () and print (), printf (), sprintf ()

① Void echo (string arg1 [, string arg2,... string argn]);

② Int print (arg );

③ Printf () can output content mixed with static text and dynamic information transmitted through variables.

Boolean printf (string format [, mixed args]);

For example, printf ("bar inventory: % d bottles of tonic water", 100 );

Output bar inventory: 100 bottles of water

Here % d is a placeholder to indicate that the output is an integer.

Placeholders:

Parameter description

% B Indicates that the parameter is regarded as an integer and displayed as a binary number.

% C considers the parameter as an integer and displays it as an ASCII character.

% D: the parameter is regarded as an integer and displayed as a signed decimal number.

% F considers the parameter as a floating point number and displays it as a floating point number.

% O considers the parameter as an integer and displays it as a signed octal number.

% S: the parameter is considered a string and displayed as a string.

% U indicates that the parameter is an integer and is displayed as an unsigned decimal number.

% X is an integer that is considered as a lowercase hexadecimal number.

% X indicates that the parameter is regarded as an integer and is displayed as a hexadecimal number in uppercase.

If you want to input two parameters

Printf ("% d bottles of tonic water cost $ % f", 100,43, 20 );

When using decimals, you can use a precision indicator to adjust the precision.

Printf ("$ %. 2f", 43.2); // $43.20

④ Sprintf ()

Similar to printf (), but it assigns the output to a string instead of the output on the browser.

String sprintf (string arg [, mixed args]);

Example: $ cost = sprintf ("$ %. 2f", 43.2); // $ cost = 43.20;

5. type conversion

(Array) to an array

(Bool)/(boolean) boolean value

(Int)/(integer) integer

(Object) object

(Real)/(float)/(double) floating point type

(String) string

Any data type can be converted to an object. The result is that the variable becomes an attribute of the object, which is named scalar.

$ Model = 'test ';

$ Obj = (object) $ model;

Echo $ obj-> scalar; // test

An integer that starts with an integer and is converted to an integer. Otherwise, the conversion result is 0.

If a string containing./e/E is used in mathematical computation, the string is calculated as a floating point.

$ Val1 = "1.2e3"; // 1,200

$ Val2 = 2;

Echo $ val1 * $ val2/2400

6. gettype (), settype ()

String gettype (mixed var) // obtain the type

Obtain the type of the variable specified by var. the return type is 8:

Array, boolean, double, integer, object, resource, string, unknow type

Boolean settype (mixed var, string type );

Set the type of the variable specified by var to the type specified by type, with 7 types:

Array, boolean, integer, float, object, null, string

7. determine the variable type

Boolean is_name (mixed var );

Is_name includes the following functions:

Is_array (), is_bool (), is_float (), is_integer (), is_string (), is_object (), is_resource (), is_null ()

Is_scalar (), is_numeric ()