Refrence to ... is ambigous!! / C++ - c++

Question

#include <iostream>
using namespace std;
class Student
{
protected:
long studentID;
public:
void setStudentID(long s_){ studentID = s_; }
Student(): studentID(0){}
long get_StudentID(){ return studentID; }
};
class Exam : public Student
{
protected:
float mark;
public:
void setMark(float m_){ mark = m_; }
Exam(): mark(0){}
float getMark(){ return mark; }
};
class Sports : public Student
{
protected:
float score;
public:
void setScore(float s_){ score = s_; }
Sports(): score(0){}
float getScore(){ return score; }
};
class Result: public Student, public Exam, public Sports
{
private:
float Total;
public:
float getTotal(){ return getMark() * getScore(); }
void display();
};
void Result::display()
{
cout << "Student ID = " << get_StudentID() << endl;
cout << "Exam Mark = " << getMark() << endl;
cout << "Sports Score = " << getScore() << endl;
cout << "Total Mark = " << getTotal();
}
int main()
{
Result st1;
st1.display();
return 0;
}
I wrote this code in Code::Blocks and it's incomplete yet , but this error that says "refrence to get_StudentID is ambigous" confused me; What's wrong with it?
Should I delete using namespace and insert std:: before all (cout, cin & endl) statments?

Answer 1

You are misunderstanding inheritance. For example, the class Exam with this line
class Exam : public virtual Student
is publicly inheriting from Student. Public inheritance should only be used in an IS-A relationship. In this case, Exam is not a Student so you shouldn't use public inheritance. Same goes for Sports.
"Call is ambiguous" means that when you call get_StudentID from Result the compiler can't decide between Exam::get_StudentID or Sports::get_StudentID which they both inherit from Student.
Instead:
Remove the inheritance, don't use inheritance anywhere here. I would completely remake this and make a Student class with Exam and Sports member objects (which can become vector of objects later if needed) and call the needed functions from the member objects instead. As a general tip, avoid multiple inheritance unless completely necessary.

Answer 2

This is an easy fix
remove Student from Results base class
make Student public virtual from both Exam and Sports class
#include <iostream>
using namespace std;
class Student
{
protected:
long studentID;
public:
void setStudentID(long s_){ studentID = s_; }
Student(): studentID(0){}
long get_StudentID(){ return studentID; }
};
class Exam : public virtual Student
{
protected:
float mark;
public:
void setMark(float m_){ mark = m_; }
Exam(): mark(0){}
float getMark(){ return mark; }
};
class Sports : public virtual Student
{
protected:
float score;
public:
void setScore(float s_){ score = s_; }
Sports(): score(0){}
float getScore(){ return score; }
};
class Result: public Exam, public Sports
{
private:
float Total;
public:
float getTotal(){ return getMark() * getScore(); }
void display();
};
void Result::display()
{
cout << "Student ID = " << get_StudentID() << endl;
cout << "Exam Mark = " << getMark() << endl;
cout << "Sports Score = " << getScore() << endl;
cout << "Total Mark = " << getTotal();
}
int main()
{
Result st1;
st1.display();
return 0;
}
Godbolt: https://godbolt.org/z/4f5n8M5of