Hybrid Inheritance - OOP's Concept

#include <iostream.h> class mm
{
protected:
int rollno;
public:
void get_num(int a)
{ rollno = a; }
void put_num()
{ cout << "Roll Number Is:"<< rollno << "\n"; }
}; class marks : public mm
{
protected:
int sub1;
int sub2;
public:
void get_marks(int x,int y)
{
sub1 = x;
sub2 = y;
}
void put_marks(void)
{
cout << "Subject 1:" << sub1 << "\n";
cout << "Subject 2:" << sub2 << "\n";
}
};
class extra
{
protected:
float e;
public:
void get_extra(float s)
{e=s;}
void put_extra(void)
{ cout << "Extra Score::" << e << "\n";}
};
class res : public marks, public extra{
protected:
float tot;
public:
void disp(void)
{
tot = sub1+sub2+e;
put_num();
put_marks();
put_extra();
cout << "Total:"<< tot;
}
};
int main()
{
res std1;
std1.get_num(10);
std1.get_marks(10,20);
std1.get_extra(33.12);
std1.disp();
return 0;
}