Stupid birds Learn PHP (ii) How to use variables

Stupid birds Learn PHP (ii) How to use variables

I. Declaration of variables

1. methods of declaring variables in PHP: $var = 123;

2. PHP is a weakly typed language, and the type of the variable is determined by the stored value

Note: Java is a strongly typed language, declaring a variable must first specify the type

3. Isset () and unset ()

Isset (): Determine whether the value exists; Unset (): Remove the value of the variable

Two. Naming of variables

1. be sure to use "$" before the variable, declare and use this symbol.

2. You cannot start with a number.

3. Cannot use the arithmetic symbol in PHP +-*/% &

4. You can use the System keyword as the variable name

5. Only variables and constants in PHP are case-sensitive, others do not differentiate

Two. Variable variable

1. variable names for a variable can be set and used dynamically

2. Variable can be referenced assignment (and a reference in Java)

Three. Types of variables

1. As mentioned earlier, PHP is a weakly typed language, and its type is determined by the stored value

2. PHP has 8 types:

2.1) Four kinds of scalars:

Shape: int integer Boolean: bool Boolean float: float double real string: string

2.2) Two types of composite

Array: Array object: Object

2.3) Special types in two

Resource type: Resource NULL type: null

 
  int (1) [1]=>int (2) [2]=>int (3)} $var =new mysqli ("localhost", "root", "root", "newcms"); Var_dump ($var); Object (mysqli) #1 (0) {} $var =fopen ("1.php", "R"), Var_dump ($var); Resource (3) of type (stream) $var =null;var_dump ($var); Null?>

Four. Variable declarations of various types

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