PHP Basics Introductory Study Notes, PHP Basics Introductory Study Notes_PHP Tutorial

Study notes for the basic introductory chapter of PHP, study notes for the introductory chapter of PHP

This article introduces in detail the most basic content in PHP learning, including basic data types and variable types. , operators and other things that everyone needs to come into contact with when getting started.
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Basic data types supported by php:
Integer: integer
Float (Double, double precision value): floating point number, representing all real numbers
String: string
Boolean: Boolean value, true/false
Array: saves multiple data items of the same type
Object: object, saves an instance of a class
NULL: has not been assigned, has been reset, or has been assigned a special value NULL variables
Specific built-in functions (such as database functions) will return variables of type resource

Four scalar types:

string (string)
integer (integer)
float (floating point type, also called double)
boolean (Boolean)
Two composite types:

array (array)
object (object)
Two special types:

resource (resource)
NULL (empty)
View variable type
You can easily check the type of a variable through the gettype() function:

Copy the code as follows
$var_bool = TRUE; // a boolean
$var_str = "foo"; // a string
$var_int = 12; // an integer

echo gettype($var_bool); // Output boolean
echo gettype($var_str); // Output string
echo gettype($var_int); // Output integer
?>

Tips
Due to historical reasons, if it is float type data, the gettype() function returns double instead of float.
If you want to view the value and type of an expression, please use the var_dump() function.
Determine the variable type
If you want to determine the next logical action by judging the variable type, do not use gettype(), but use the is_type series of functions:

The code is as follows Copy code
$var_int = 12;

// If $var_int is int type, this is added
if (is_int($var_int)) {
$var_int = $var_int 4;
}
echo $var_int; // Output 16
?>

Both NULL and resource represent external resources, such as database connections
Basically, a resource variable cannot be directly manipulated, but usually they will be returned by the function and must be passed as parameters to other functions.

In PHP, the type of a variable is determined by the value assigned to the variable. (Dynamic type language)
PHP can determine the type of a variable at any time based on the value stored in the variable, that is, it has the function of transparently changing the variable type at any time.
PHP will "automatically" get the input data type and once the variable value is retrieved from the variable, it will return data with the same data type.
Make it a habit: Constant names are composed of uppercase letters. This makes it easier to distinguish between variables and constants.
An important difference between constants and variables is that when referencing a constant, there is no $ sign in front of it.
Another difference between constants and variables is that constants can only store Boolean values, integers, floating point numbers or string data, and these types are all scalar data.

Variable type change (juggling)
PHP does not need (or does not support) to specify its variable type in the declared variable; the type of a variable is determined by the context in which the variable is used, that is to say , if you assign a string value to a variable var, var becomes a string variable. If you assign an integer to var, it becomes an integer variable. An example of PHP automatically converting variable types is the addition operator ' '. If any operand is a double, then all operands are evaluated as doubles, and the result is also a double. Otherwise, the operands will be considered to be integers and the result will be an integer. Note that this does not affect the variable type of each operand itself, the only change is how the operands are processed during the calculation. $foo = "0"; // $foo is a string, the value is "0" (ASCII 48)

PHP code

Copy the code as follows
$foo = "http://www.hzhuti.com/HTC/G11/"; // $foo is a string, the value is "0" (ASCII 48)
$foo ; // $foo is a string with the value "1" (ASCII 49)
$foo = 1; // $foo is now an integer (2)
$foo = $foo 1.3; // $foo is now a double (3.3)
$foo = 5 "10 Little Pigs"; // $foo is an integer (15)
$foo = 5 "10 Small Pigs" "; // $foo is an integer (15)

If you think the last two expressions in the above example look a bit strange, please see the "String Conversion" section. If you wish to force a variable to be evaluated as a fixed type, see the "Casting" section. If you wish to change the type of a variable, please see the description of the function "settype()".
Determining the type of a variable
Because PHP determines the type of variables itself and generally converts them as needed, the type of a particular variable is not always obvious. PHP includes functions to find out the type of this variable. These functions are gettype(), is_long(), is_double(), is_string(), is_array(), and is_object().
Type casting (type casting)
Type casting in PHP is the same as in C language It's roughly the same: write the required type in parentheses before the variable to be coerced.

PHP code

The code is as follows Copy code
$foo = 10; // $foo is an integer
$bar = (double) $foo; // $bar is a double precision number

The following coercion methods are allowed: (int), (integer) - coerce to integer (real), (double), (float) - coerce to double precision number (string) - coerce to string (array) - coerce to array (object) - coerce to object Note that tabs and spaces are allowed within parentheses, so the following statements are equivalent: $foo = (int) $bar; $foo = ( int ) $bar;
String conversion
When a string is evaluated as a numeric value, its result and type are determined as described below. If this string contains the characters '.', 'e', ​​or 'E', it is treated as a double type variable, otherwise it is treated as an integer. The value of this string is determined by the prefix. If the string begins with any valid numeric data, then the numeric data is the value on which the string is evaluated. Otherwise, the value is zero. Valid numeric data follows the following notation, followed by one or more digits (which may include a decimal point), followed by an optional exponent. The exponent is formed by one or more digits followed by 'e' or 'E'.

PHP code

The code is copied as follows
$foo = 1 "10.5"; // $foo is a double precision number (11.5)
$foo = 1 "-1.3e3"; // $foo is a double precision number (-1299)                                                                                                                                                    $ foo‑ ‑‑‑ ‑‑ $foo = 1 "10 Small Pigs"; // $foo is an integer (11)
$foo = 1 "10 Little Piggies"; // $foo is an integer (11);
// this string Contains the character 'e'


Identifier

operator:

1) Assignment operator: =

2) Arithmetic operators: , -, *, /, % (modulo)

3) Connection operator: ., no matter what the operand is, it is treated as String, and the result returns String

4) Combined Assignment Operators: =, *=, /=, -=, %=, .=

5) Automatically Incrementing and Decrementing:

(1) $variable =1 ⇔$variable; $variable-=1 ⇔$variable-, just like the c language, do other operations first, then or-

(2) $variable, -$variable, first or -, then do other operations

6) Comparison operator:

= = (left side equals right side),! = (the left side is not equal to the right side),
= = = (the left side is equal to the right side, and the data type is the same),
>=, >, <, <=

7) Logical operators: || or, && and, xor (when one and only one of the left and right sides is true, return true), !

A reference table

Operator (Arithmetic Operators) Operator
Symbol Description
DescriptionExample
Case Result
Result
Addition
Plus sign x=2
x 2 4
- Subtraction
Minus sign x=2
5-x 3
* Multiplication
Multiplication sign x=4
x*5 20
/ Division
Division sign 15/5
5/2 3
2.5
% Modulus (division remainder)
Modulus (remainder) 5%2
10%8
10%2 1
2
0
Increment
increase x=5
x x=6
-- Decrement
decrement x=5
x-- x=4

Assignment Operators
Assignment Operators

Operator
SymbolExample
Case Is The Same As
is equivalent to
= x=y x=y
= x =y x=x y
-= x-=y x= x-y
*= x*=y x=x*y
/= x/=y x=x/y
%= x%=y x=x%y

Comparison Operators
Comparison Operators

Operator
Symbol Description
Specific descriptionExample
case
== is equal to
equal to 5==8 Return false
!= is not equal
not equal 5!=8 returns true
> is greater than
greater than 5>8 returns false
< is less than
less than 5<8 returns true
>= is greater than or equal to
greater than or equal to 5>=8 returns false
<= is less than or equal to
less than or equal to 5<=8 returns true

Logical Operators
Logical Operators

Operator
Symbol Description
DescriptionExample
Case
&& and
with x=6
y=3
(x < 10 && y > 1) Return true

|| or
or x=6
y=3
(x==5 || y==5) Return false

! not
Not x=6
y=3
!(x==y) returns true

Other operators:

Ternary operator, error suppression operator, execution operator, array operator, type operator

Expression before operator "?"

If an expression containing a binary operator appears before the "?" of the ternary operator "? :", then a pair of parentheses should be added to the expression. For example:
(x >= 0) ? x : -x;

Let’s look at a simple one? Number expression example

The code is as follows Copy the code

$a='http://www.zhutiai.com/zhuti/c7/';

echo $a?'true':'false';

The output result is trur;

See you again

if( $a )

{

echo 'true';

}

else

{

echo 'false';

}

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