Need help in Virtual functions ; Can't figure out the error

Question

#include <iostream>
using namespace std;
class health{
protected:
int power;
public:
virtual void newhealth(int);
};
class apple:public health{
public:
void newhealth(int a){
power =a;
cout<<"Eating an apple will increase your health by "<<power<<endl;
}

};
class banana:public health{
public:
void newhealth(int a){
power =a;
cout<<"Eating an banana will increase your health by "<<power<<endl;
}

};
int main()
{
apple a;
banana b;
health* fruit1=&a;
health* fruit2=&b;
fruit1->newhealth(25);
fruit2->newhealth(10);

return 0;
}

Answer 1

In class healt:
virtual void newhealth(int) = 0;
You need to tell compiler that function newhealth has no body ( = 0 )