PHP Knowledge points-data types and operators

First, the data type

A, the whole division
Scalar type: int--reshape, float--decimal, string--string, bool--Boolean two values
Composite type: Array, object
Special type: null, resouce

2, integer type int, an integer

3, 3 kinds of integer notation
Decimal notation: 123:
$n 1 = 123;
Octal notation: 0123
$n 2 = 0123;
Hexadecimal notation: 0x123
$n 3 = 0x123;

4. Floating-point type: float, double, real

There are two ways to do this:
$v 1 = 1.234; With a decimal point, which is the floating type
$v 2 = 1.234e3;//means: 1.234 times 10 of 3 times, or 1234, with E in the form of floating-point numbers
$v 3 = 1234e3;//The result value is 1234000, but it is also a floating-point number.
Note: Floating-point numbers should not be compared directly to size
The usual practice: multiply the number of digits by 10, for example, the precision requires 3 digits, then multiply by 103 times the square
When the result of an integer operation exceeds the range of an integer, it is automatically converted to a floating-point number.

5. String type: string

6. Boolean type:bool, Boolean

7. Array type: Arrar

8, Object Type objects : usually refers to their own definition of the object, pure grammar.

9. Resource type resource: refers to a reference to external data.

10, NULL type NULL

B, type conversion
A, auto-conversion: It converts data that is not handled by the operator into data that can be processed, depending on the needs of the operator in various operations.
if (data) {}: converted to bool type
Arithmetic operators: converting to numeric types
Join operators: Convert to String type
Comparison operator: To Boolean type or numeric type
If there is at least one boolean on both sides, the other side will turn to Boolean and compare
Otherwise, the comparison is converted to a number
A particularly common conversion, whether auto-cast or cast, is to convert the string to a number:
"5" ==>> 5//integer
"5.5" ==>> 5.5 floating point
"5abc" ==>> 5 integers
"5.5ab" ==>> 5.5 floating point
"Abc5" ==>> 0 integers
"abc" ==>> 0 integers
"" ==>> 0
Start from the left until the first character that is not a number ends

B, cast : It is the syntax to convert a data to another type of data
Output data type:
The ability to output the full information of a variable: var_dump ()
Gets the type name of a variable: GetType ()
Isset (), Empty (), unset ();
Isset () Determines whether a variable has data:
Empty () to determine whether a data is empty: close to our daily concept (Nothing is empty)
Unset (): Destroys (deletes) a variable.
IS_XX type () series function: Determines whether a data is of a certain type, including:
Is_int (), Is_float (), Is_numeric (), Is_bool (), Is_array (), Is_scalar ()--detects if a variable is a scalar:
Is_numeric () to: 3, 3.5, "3", "3.14" is true
Is_scalar (): Determines whether it is a scalar type (that is, Int,float,stirng,bool)

Second, operator

1. Arithmetic operators
There are several: +-*/% + +--
Note: Pay attention to the remainder operation%, first take the whole, then take the remainder
$v 1 = 7.5 3; The result is: 1
$v 2 = 7.5 3.5; The result is: 1

2. Self-increment decrement operator:
General: The number is self-added 1 or self-minus 1.
String: Only self-increment, and the effect of self-increment is "next character"
Boolean Increment decrement invalid
Null decrement is invalid, increment result is 1

3, pre-Gaga and post-gaga differences:
Before + +: The increment operation of the variable is done first, then the value of the variable is taken to participate in other operations.
Post + +: Store The value of the original variable temporarily, increment the value of the variable, and then participate in another operation with the temporarily stored value.

4. Comparison operators:

Include:> >= < <=! = = = value Size comparison (judging) = = = value size and data type are compared!==
The difference between = = and = = =:
= = Comparison of value size (judging)
= = = value size and data type are compared

5. Shift Operators
Left-shift Operation:<< a << n;//a is a number to be moved, it can also be a normal number, but by binary, n is a specified number of bits to move
Right-shift Operation:>> a >> n;//a is a number to be moved, it can also be a normal number, but by binary, n is a specified number of bits to move

6. Condition (trinocular) Operator:
A generic operator requires 2 data to participate
There are several operators that require only one data participation: + +,--!
The
A conditional operator requires at least 3 data to participate!
The form is:
Data 1? Data 2: Data 3
Typically, data 1 should eventually be a Boolean value (if not, it will be used as a Boolean value).

Meaning:
If data 1 is true, the result of the operation is data 2, otherwise the result of the operation is data 3

7. Error control Operator:@ is usually used in front of an expression "possibly" where the error occurred-the most common scenario is to connect to the database.

PHP Knowledge points-data types and operators