Classes and inheritance

Question

jdpjtp910 0 Light Poster

16 Years Ago

Ok, I have a class project to basically design a program that handles classes and vehicles. What I have so far is far from the ending product. I have made 3 classes, car, vehicle, and motorcycle. Car and motorcycle are dervied from vehicle. The car class has a set const variable for number of wheels to 4. mpg and model name are the other variables. Motorcycle is a class with const for 2 wheels and model and mpg. Vehicle only has number of wheels and mpg.

Here is my code thus far.

Class: car.h

#ifndef CAR_H
#define CAR_H

#include <string>

#include "vehicle.h"

using std::string;

class Car  : public Vehicle {
public:
  Car();
  Car(string const& model, double milesPerGallon);

  void setModel(string const& model);

  string const& getModel() const;

  virtual void print() const;

private:
  string model;
};

#endif

Class motorcycle.h:

#ifndef MOTORCYCLE_H
#define MOTORCYCLE_H

#include <string>

#include "vehicle.h"

using std::string;

class MotorCycle : public Vehicle {
public:
  MotorCycle();
  MotorCycle(string const& model, double milesPerGallon);

  void setModel(string const& model);

  string const& getModel() const;

  virtual void print() const;

private:
  string model;
};

#endif

class vehicle.h

#ifndef VEHICLE_H
#define VEHICLE_H

class Vehicle {
public:
  Vehicle();
  Vehicle(int wheels, double milesPerGallon);

  void setWheels(int wheels);
  void setMilesPerGallon(double milesPerGallon);

  double getMilesPerGallon() const;
  int    getWheels() const;

  virtual void print() const;

private:
  int wheels;
  double milesPerGallon;
};

#endif

source files:
car.cpp:

#include "car.h"

#include <iostream>

using namespace std;

Car::Car() {
}

Car::Car(string const& model, double milesPerGallon)
    : Vehicle(4, milesPerGallon), model(model) {
}

void Car::setModel(string const& model) {
  this->model = model;
}

string const& Car::getModel() const {
  return model;
}

void Car::print() const {
  Vehicle::print();
  cout << "Car model: " << model << "\n";
}

motorcycle.cpp

#include "motorcycle.h"

#include <iostream>

using namespace std;

MotorCycle::MotorCycle() {
}

MotorCycle::MotorCycle(string const& model, double milesPerGallon)
    : Vehicle(2, milesPerGallon), model(model) {
}

void MotorCycle::setModel(string const& model) {
  this->model = model;
}

string const& MotorCycle::getModel() const {
  return model;
}

void MotorCycle::print() const {
  Vehicle::print();
  cout << "Motorcycle model: " << model << "\n";
}

vehicle.cpp

#include "vehicle.h"

#include <iostream>

using namespace std;

Vehicle::Vehicle() {
  wheels = 0; milesPerGallon = 0;
}

Vehicle::Vehicle(int wheels, double milesPerGallon)
  : wheels(wheels), milesPerGallon(milesPerGallon) {
}

void Vehicle::setWheels(int wheels) {
  this->wheels = wheels;
}

void Vehicle::setMilesPerGallon(double milesPerGallon) {
  this->milesPerGallon = milesPerGallon;
}

double Vehicle::getMilesPerGallon() const {
  return milesPerGallon;
}

int Vehicle::getWheels() const {
  return wheels;
}

void Vehicle::print() const {
  cout << "Wheels number: " << wheels << "\n"
    << "Miles per gallon: " << milesPerGallon << "\n";
}

and main.cpp

#include <iostream>

#include "car.h"
#include "vehicle.h"
#include "motorcycle.h"

using namespace std;

int main() {
  double mpg; 
  int wheelss;
  Car c("Ford", 8);
  MotorCycle mc("Bike", 5);
  

  
  cout << "Please enter the miles per gallon for vehicle:" << endl;
  cin >> mpg;
  Vehicle milesPerGallon(double mpg);
  cout << "Please enter the number of wheels for the vehicle:" << endl;
   cin >> wheelss;
  Vehicle wheels(int wheelss);

 
  Vehicle.print();
  c.print();
  mc.print();

  return 0;
}

Problem I am having is getting users to input the code instead of having it statically held by the program. So i am attempting this with the vehicle class. I am prompting for mpg and number of wheels. when I compile I get the follow error:
Error 1 error C2143: syntax error : missing ';' before '.' \Desktop\vehicle\main.cpp 25 test15
Error 2 error C2143: syntax error : missing ';' before '.' \Desktop\vehicle\main.cpp 25 test15

I tried googleing the error and found that it typically has something to do with omission in previos lines. I have checked previous lines and have semi colons through out. Any help/guidance would be great.

THank you in advance for your time and effort!

c++

3 Contributors
2 Replies
133 Views
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Latest Post 16 Years Ago Latest Post by corby

Dani AI

Generated 9 Months Ago

The compiler error stems from statements that the compiler treats as function declarations rather than object creation. As noted, a line that looks like Type name(param-list); is parsed as a prototype (the classic "most vexing parse"), so no object is constructed and a later attempt to call a method on a non-existent instance yields the "missing ';' before '.'" message. See the cppreference explanation for the most vexing parse: .

Two straightforward fixes:

Construct a Vehicle instance with the user values, or
Default-construct an instance and then call setters.

Example patterns (use whichever fits the class API):

Vehicle v;                 // default ctor
v.setMilesPerGallon(mpg);
v.setWheels(wheelss);
v.print();                 // call on instance, not on the type

or

Vehicle v2(wheelss, mpg);  // direct construction (wheels first)
v2.print();

Additional notes and best practices:

Print is non-static; always call it on an object (e.g., v.print()), not on the class (Vehicle.print()).
Keep parameter order straight: the Vehicle ctor expects (int wheels, double mpg).
Give clear variable names (avoid typos like wheelss) to reduce confusion.
If polymorphism and containers of mixed vehicles are planned, add a virtual destructor to the base class to avoid undefined behavior:

virtual ~Vehicle() {}

’s suggestion to move I/O and construction into small helper functions (so main just orchestrates calls) is a good next step for cleaner design and easier testing.

All 2 Replies

Sky Diploma 571 Practically a Posting Shark

16 Years Ago

Vehicle milesPerGallon(double mpg);
  cout << "Please enter the number of wheels for the vehicle:" << endl;
   cin >> wheelss;
  Vehicle wheels(int wheelss);

You are declaring function prototypes here. where-as i think, you need to call the functions there. Guess you should probably check that out!

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corby -4 Junior Poster · Answer 1 · 2010-04-14T21:45:07+00:00