Calling correct virtual methods - c++

Question

Here is my code:
#include <iostream>
#include <string>
using namespace std;
class Sport{
protected:
string name;
double hours;
virtual double returnCalories()=0;
public:
Sport():name("Not defined"),hours(0.0){}
Sport(string n, double c):name(n),hours(c){}
virtual ~Sport(){}
void setName(string x){
name=x;
}
void setTime(double x){
hours=x;
}
};
class Running:public Sport{
public:
static const int CALORIES = 950;
Running(){}
~Running(){}
double returnCalories(){
return hours*CALORIES;
}
};
class Activity{
public:
Sport* one;
Activity(){}
Activity(string n,double time){
one->setName(n);
one->setTime(time);
}
~Activity(){}
};
class Diary{
private:
Activity list_activity[10];
int counter_activity;
public:
Diary():counter_activity(0){}
~Diary(){}
void addActivity(Activity x){
// add activities
}
double sumCalories(){
for(int i=0;i<10;i++){
if(list_activity[i].one->getName()=="Running"){
// I want to call returnCalories() of class Running
}
}
}
};
int main() {
Activity test("Running",3.2);
Diary test2;
test2.addActivity(test);
return 0;
}
Now I have a question:
How is it possible to call returnCalories() of class Running where I want to ? ( it's commented in the code )
Is this even possible, or should I change my logic somehow ?

Answer 1

It's crashing because you have not initialized Sport *one; and you're attempting to call methods on a null pointer. You need to first create a Running object within the Activity constructor using the "new" operator like so:
one = new Running(n, time);
Create an overloaded constructor in your "Running" class that takes the appropriate arguments as well, so that you can initialize your variable as shown above.