C++ implicit type conversion, explicit type conversion (mandatory type conversion)

1. Implicit type conversion
   1. When two variables of different types are operated, such as

   int a=1;
   double b=3.0;
   double c = a+b; //会把int转换成double再运算
   

   2. When the expression return type is different, or the function return type is different

   int a = 3.6+2.3;
   

   For example, the return type of a function is Int, but if you return a double type, it will be implicitly converted to int for you

2. Mandatory type conversion
   1, C style (commonly used)
   the type inside the brackets, or the data inside the brackets

   int a=6;
   //下面两种都行，都是C方式
   double b = double(a) * 2;
   double c = (double)a * 3;
   

   2. C++ mandatory type conversion (4 types)
   (1) static_cast<>() Static conversion, completed at compile time (recommended)

   int a=10;
   double b = static_cast<double>(a) * 3;
   

   It can be used to convert ordinary variables above, cast subclasses to parent classes, and convert void* type pointers to other types of pointers
   (2) dynamic_cast<>(): The operation is to check the conversion, and the parent class can be converted to a subclass, and the conversion cost Very large
   (3) const_cas<>()t: Remove the const attribute of pointers and references , and can remove the const attribute

   const int* p1;
   int* p2 = const_cast<int*>(p1);
   

   (4) reinterpret_cast<>()
   can even convert between different types, turn int into pointer, and turn int pointer into double pointer, which is very dangerous and should be used less