• In C language, one often use the macro way to define a constant number; in CPP, we often use const keyword.

# define VALUE 100 //C style
const int value = 100; // CPP style

• A confusing part of const occurs with point.

const int * p_int;
int const * p_int;

int * const p_int;

const int *means a pointer points to a const int; therefore the value of pointer points to cannot be changed. int const * means the same thing. While int * const means a int * pointer with const value, so that the real value (the address) of the pointer cannot be changed.

In the input of a function, we sometimes use const in or const int * to make others to believe that this function will NOT change the value of place where the pointer points to.

void func(const int *);
void func(const int &);

In a class, we may have const member and const function. A const member is just a member with const definition. A const function is a member function that cannot change the value of member variable. For example, the following codes should be a compilation error.

class Student
{
private:
    const int BMI = 24;
    int born;
public:
    int getBorn() const
    {
        born++; //compilation error
        return born;
    }
}