Automatic conversion and cast

The types of variables can be converted to each other , Conversion is divided into automatic conversion and forced conversion .

Automatic conversion rules ：

• 1、 If the type of computation involved is different , First convert to the same type , And then you do the math .
• 2、 The conversion proceeds in the direction of increasing data length , To ensure that the accuracy does not decrease . Such as int The type and long Type operation , The first int Quantity into long Type and then do the operation .   

          a、 If the number of bytes of the two types is different , Convert to a type with a high number of bytes    

          b、 If the number of bytes of the two types is the same , And a sign , An unsigned , Then convert it to Unsigned type

•  3、 All floating-point operations are performed with double precision , Even if it only includes float Expression of single precision operation , It also needs to be converted into double type , Do some more calculations .
•  4、char The type and short When type is involved in the operation , It must be converted to int type .
•  5、 In assignment operations , The data types of the quantities on both sides of the assignment number are different , Assignment number The type of the right quantity will be converted to the type of the left quantity .

            If the data type length of the quantity on the right is longer than that on the left , Some data will be lost , This will reduce the accuracy :

int a=1;
double b=2.5;
a=b;
cout << a; // Output is  2, Missing decimal part 

int a = 1;
double b = 2.1;
cout << "a + b = " << a + b << endl;  // Output is a + b = 3.1

Cast rules ：

Casts are enforced through Type conversion operations To achieve .

Its general form is ：（ Type specifier ）（ expression ） Its function is to cast the operation result of an expression into the type represented by a type specifier .

int a = 1;
double b = 2.1;
cout << "a + b = " << a + (int)b << endl;  // Output is a + b = 3