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Variable ： Variables are storage space in memory , The quantity that often changes is stored in the space, which is called variable .

classification ： integer constants 、 Floating-Point Literals 、 character constants 、 Boolean Literals 、 String constant

Define format ： data type Variable name = initialize value

Such as ：  int   a   = 1;

Variable considerations ：

1. Variable name cannot be defined repeatedly

2. A statement can define multiple variables , Separated by commas

3. Variables must be assigned before use

4. Definition float and long Variable considerations

5. Scope of variable

Constant ： During program execution , The amount whose value will not change is called a constant

data type ： The minimum information unit of a computer storage device is bit（ position ）, And the smallest storage unit is called byte（ byte ）.

1byte=8bit

 

Implicit conversion : Assign a value or variable that represents a small range of data to another variable that represents a large range of data .

Small data types , And large data types , The small one will be promoted to the big one , recompute .

byte short char Three kinds of data in operation , Whether or not there are higher data types , Will be promoted to int, And then we do the calculation .

Display conversion ： Assign a value or variable that represents a large range of data to another variable that represents a small range of data .

Format ： Target data type Variable name = ( Target data type ) Value or variable name ;

 

 

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