Multilevel 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:\n"<< 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 res : public marks
{
protected:
float tot;
public:
void disp(void)
{
tot = sub1+sub2;
put_num();
put_marks();
cout << "Total:"<< tot;
}
}; int main()
{
res std1;
std1.get_num(5);
std1.get_marks(10,20);
std1.disp();
return 0;
}