Derived class cannot access private area of base class

example:

#include <iostream>

using namespace std;

class BASE{
    public:
        void doit();
        int a;
    protected:
        int b;
    private:
        int c;
};

class DERIVED:public BASE{
     public:
        void doit();
};

void BASE::doit(){
    cout << "BASE::doit()" << endl;
    cout << a << endl;
    cout << b << endl;
    cout << c << endl;
};

void DERIVED::doit(){
    cout << "DERIVED::doit()" << endl;
    BASE::doit();
    cout << "---" << endl;
    cout << a << endl;
    cout << b << endl;
    cout << c << endl;  //ERROR: cannot access private of base class

}

int main()
{

    BASE base;
    base.doit();
    DERIVED derived;
    derived.doit();
    return 0;
}