Detailed explanation of php5 and mysql5 web development technology-3 variables, expressions and constants_PHP tutorial

1. Definition, naming and classification

Divided into three types: scalar variables, array variables and objects

2. Printing and output variables

echo statement

printf() function

          Example: ：

                                                                        printf("%d bootles of beer on %s", 100, "the wall");

printf("The %2$s likes to %1$s", "bark","dog");

sprintf() function

Example:

$formatted= fprintf("%01.2f",$var);

3. Display arrays and objects

print_r(array and variable);

var_dump (array variable object)

var_export (array variable object) The representation of the variable can be returned by setting parameters

          Example:

　$v = var_export($a,true); //Return the source code of php and use it directly in the array of php script

4. Data types supported by php variables

Integer, double, character, Boolean

Array, object, resource(Resource)

NULL

There are two ways to quote strings: double quotes and single quotes

Get and set variable type: gettype()/settype()

Arrays and objects are called conforming data types

5. Variables of variables

$var_name = 'php5';

$$var_name = ''php5 web development details;

echo $php5;

6. Super global variable array

$_GET[]

$_POST[]

$_COOKIE[]

$_SESSION[]

$_ENV[]

$_SERVER[]

$_FILES[]

$_REQUEST[]

$_GLOBALS[]

7. Variable operator

There is a lot of content, only the categories are listed without specific enumeration.

Arithmetic

Assignment

String concatenation

Pre and post addition and subtraction

Reference & After reference assignment, the variables have the same memory address

Ternary operator

Comparison operation

Boolean operator

Bit operator

Other operators:

1. Error suppression @

2. External command execution

                    $out = ·dir c:·

                      print_r($out);  

                    $our = shell_exec("dir");

echo $out;

The results of the two functions are the same, and the result is placed in a array; shell_exec () method puts the result in a scalar variable

8. Variable and script processing

isset()

unset()

empty()

is_array()is_integer()is_numeric()

9. Data conversion

Force type conversion of variables:

(array)

(bool)/(boolean)

(int)

(object)

(real)/(double)/(fload)

(string)

Others:

(1)intval($var):

(2)HereDoc

HereDoc allows embedding some large text content in php, such as email templates or some html or text content.

$string = 'hello';

$output = <<

The value of $string in HEREDOC is $string

MYDOC

echo $output;

The output result is: the value of $string in HEREDOC is hello

(3) escape character

n, t , \ ,$ ,''

(4) Numeric conversion function

chr($var) : Return the corresponding ASCII character according to the value of $var;

ord($string) returns the ASCII code value of the first character of the string;

10. Constant definition and magic constants

define("CONSTANT_NAME", constant value)

__LINE__

__FILE__

__FUNCTION__

__CLASS__

__METHOD__

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