Efficiency of Car

#include <iostream>
using namespace std;
class Car
{
  public:
  float startMiles, endMiles, litres;
  int perlitre;
  void initializeData(float s,float e,float l)
  {
    cin>>startMiles>>endMiles>>litres;
  }
  float getstartMiles()
  {
    return startMiles;
  }
  float getEndMiles()
  {
    return endMiles;
  }
  float getLitres()
  {
    return litres;
  }
  double calculateMPL()
  {
    perlitre = (endMiles-startMiles)/litres;
    return perlitre;
  }
  string isEconomycar()
  {
    if(perlitre>18)
      return "true";
    else if(perlitre<18)
      return "false";
    else
      return "Improper readings";
  }
};
int main()
{
    Car obj;
    float a, b, c;
    obj.startMiles;
    obj.endMiles;
    obj.litres;
    obj.perlitre;
  obj.initializeData(a, b, c);
    if(obj.calculateMPL()>=0)
    {
      cout<<obj.getstartMiles()<<endl;
      cout<<obj.getEndMiles()<<endl;
      cout<<obj.calculateMPL()<<endl;
      cout<<obj.getLitres()<<endl;
      cout<<obj.isEconomycar()<<endl;
    }
    else
      cout<<"Improper readings"<<endl;
    return 0;
}