Basic knowledge of PHP (2)

December 9, 2016, Friday

first, Types of Variables:

1. Basic Type:

Integral type (integer);

Float type (float);

Strings (string);

Boolean type (boolean);

2. Composite type:

Arrays (array);

Objects (object);

3. Special Type:

NULL

Resource Type resource;

Note: if a string and a number are added, the string is automatically converted to a pure number, and then the addition is DONE.

If the strings are added, they are automatically converted to numbers and then Added.

second, variable:

definition: $ variable name;

note: variable name: can only be letters, numbers, underscores, cannot start with a number

Custom variables are case-sensitive

Writing variables: using small humps (onetwothree)

three, constant:

define ("constant name", constant value);

Note: The constant name is generally all uppercase;

Constant name: only letters, numbers, underscores, constant names cannot begin with a number, and can only be assigned once.

Iv. the difference betweenisset () and empty () :

Empty () determine if the value of a variable that has been defined is null {', 0, 0.0, [], false, ' 0 '}

isset () Determines whether a variable has a value (initialized );

v. Type conversion methods:

first: Change the value only, the type of the variable is the same

(type) $ variable Name

$a = ' 123abc ';

$b = (int) $a;

Echo $b;

Second: variable types are changed

Settype ($ variable name, "type")

$a = ' 123abc ';

$b = Settype ($a, "integer");

Echo $b;

Third: use system-provided functions (val-family Functions) to change only the value, without changing the variable type

boolval ($ variable Name)

doubleval ($ variable Name)

Floatval ($ Variable Name)

intval ($ variable Name)

strval ($ variable Name)

Basic knowledge of PHP (2)