One of PHP introductory study notes_PHP tutorial

1. Basic syntax
The way to embed a PHP script in HTML code is to write the code in . Output data to the browser using the echo or print function. echo can accept multiple parameters, print can only accept one. The form of echo is

void echo(string arg1,[,...string argn]);

PHP syntax allows the omission of parentheses. For example,

will output Hello my world on the browser

PHP also supports a and C language A very similar printf function, such as printf(' %d apples',100), will output 100 apples. The usage of sprintf is the same as printf, but instead of outputting to the browser, it returns a string.

2. Data types and variables

PHP is weakly typed. A variable does not need to be declared in advance, nor does it need to specify a type. Variables in PHP are $ plus the variable name. PHP variables are case-sensitive. For example, $my='my' in the above example.

The variable types supported by PHP include: Boolean, integer, floating point, string, array and object. The first four are very commonly used and are similar to other languages, so I won’t introduce them in detail. Arrays and objects will be introduced in detail later.

There are functions in PHP to detect the type of objects, they are getttype. gettype returns a string whose value can be array, boolean, double, integer, object, resource, string and unknown type. PHP also supports explicit type conversion, and the syntax is similar to C. The

conversion operator converts to
(array) array
(bool) (boolean) boolean
(int) (integer) integer
(object) object
( float), (double), (real) floating point number
(string) string

For example:

The output result is:

string
integer
string
double

There are also functions that can be used to determine whether a variable is of a certain type, such as is_array(), is_bool(), etc. The usage is similar.

3. Function and variable scope
The method of declaring functions in PHP is very simple, in the following form:

No need to specify the return type , there is no need to specify the variable type in the brackets, as long as there is a variable name. For example:

By default, PHP Parameters are passed by value. Changing the value of the parameter within the function will not change the value of the variable outside the function. However, PHP also supports passing by reference. The syntax is consistent with C, &$paramName. For example, the following is a classic example:

Output result:

a is 3, b is 5
a is 5, b is 3

PHP functions also support default values ​​for parameters, and the syntax is the same as C. For example:

The scope of variables is introduced below. PHP's variable scope is very similar to C. There are four types: local variables, function parameters, global variables, and static variables. Local variables are variables declared within the function, and function parameters are variables declared at the beginning of the function; variables not declared in the function are global variables, and global variables can be accessed anywhere, but unlike C, if they are in a function To modify the value of a global variable, you need to explicitly specify it as a global variable using the GLOBAL keyword, otherwise PHP will declare a local variable with the same name and overwrite it. For example:

The output result is:

0.03

1.03

PHP also has a super global variable. Super global variables are predefined by the PHP system and are mainly used to access environment-related information, such as the current user session, user operating environment and local environment. The super global variable is an array. For example, $_SERVER stores server-related information. $_GET, $_POST, $_FILES, and $_COOKIE respectively store information submitted by the client using get and post, uploaded files, cookie information, etc. The use of these variables is very simple. If you need any information, you only need to look up

4. The variables of variables
are different from static languages ​​such as C. The variable name of PHP itself can be a Variables, which are very convenient when many variables need to be generated dynamically. For example:

The output result is: I am hello


5. Flow control statements
mainly include, if else, while, for, do while, switch. These are very similar to C language and are basically the same. Not much introduction. There are some differences. PHP's elseif is a keyword that is connected together, while C language is else if.