polymorphism

[nikman]

i am writing this code which involves an eatery type class and 2 derived classes
snackcart and restaurant. how can i implement polymorphism in this? i want to make use of dynamic objects.

eatery.h

#ifndef EATERY_H
#define EATERY_H
#include <string>
#include <vector>
#include "meals.h"
using std::string;
using std::vector;

class Eatery {
    public:
		Eatery();
		~Eatery();
        virtual void setOwner(string name) = 0;
        virtual string getOwner() = 0;
	
	protected:
		string owner;
		Meal *meals;
		int size;
		
};
#endif 

snackcart.h

#ifndef _SNACKCART
#define _SNACKCART
#include "eatery.h"

#include <string>
#include <vector>
using std::vector;
using std::string;


class SnackCart: public Eatery {
    public:
        SnackCart();
		~SnackCart();
		void setOwner(string name);
		string getOwner();

        void setLocation(string location);
        string getLocation();
		
		void setMealArray(int);

        void clearMeals();
        void addMeal(string name, float cost,string ratingStr);
		void loadaddMeal(string name, float cost,string ratingStr);
        int mealCount();

        int getMealNames(string names[]);
        float getMealCost(string name);
        string getMealRatingForName(string name);
        string getRatedMeal(string ratingStr);
        RatingType getRating(string str);

        void adjustMealCost(string name, float cost);
        void adjustMealRating(string name, RatingType rating);

        string cheapestMeal();
        string mostPopularMeal();

        void displayCartDetails();

    private:
		vector<Meal> meal;
        int findMeal(string name);
        string location;
        int count;
};

#endif 

restaurant.h

#include "eatery.h"
#ifndef RES_H
#define RES_H

class Restaurant: public Eatery
{
	public:
		Restaurant();
		~Restaurant();

        void setResName(string name);
        string getResName();

        void setAddress(string address);
        string getAddress();

		void setPhoneNo(int phone);
		int getPhoneNo();

		void setOpeningHour(string openHr);
		string getOpeningHr();

		void setMealArray(int);
		
        void clearMeals();
        void addMeal(string name, float cost,string ratingStr = "Unknown");
        int mealCount();

        int getMealNames(string names[]);
        float getMealCost(string name);
        string getMealRatingForName(string name);
        string getRatedMeal(string ratingStr);
        RatingType getRating(string str);

        void adjustMealCost(string name, float cost);
        void adjustMealRating(string name, RatingType rating);

        string cheapestMeal();
        string mostPopularMeal();

        void displayRestaurantDetails();

    private:
		vector<Meal> meal;
        int findMeal(string name);
        string address;
        int count;
	
};

snackcart.cpp
[code]
#include "snackcarts.h"

#include <iostream>
#include <vector>
using std::vector;
using std::cout;
using std::cin;
using std::endl;

SnackCart::SnackCart() : Eatery(){
	meal.resize(100);
	owner = "Unset";
    location = "Unknown";
    count = 0;
}

void SnackCart::setOwner(string name) {
    owner = name;
}

string SnackCart::getOwner() {
	return owner;
}

void SnackCart::setMealArray(int size_of_array)
{
	size = size_of_array;
	meal.resize(size);
}

void SnackCart::setLocation(string name) {
    location = name;
}

void SnackCart::clearMeals() {
    count = 0;
}

void SnackCart::addMeal(string name, float cost,string ratingStr) {
    
    if (count == size) {
        cout << "Done." << endl;
        return;
    }

    meal[count].setName(name);
    meal[count].setCost(cost);
    meal[count].setRating(Meal::ratingType(ratingStr));
    ++count;
}


void SnackCart::loadaddMeal(string name, float cost,string ratingStr) {
    
	meal[count].setName(name);
    meal[count].setCost(cost);
    meal[count].setRating(Meal::ratingType(ratingStr));
    ++count;
}

int SnackCart::findMeal(string name) {
    if (count == 0) { // empty list
        return size; // force return value to be bigger than count
    }
    int i;
    for (i = 0; i < count; ++i) {
        if (meal[i].getName() == name) {
            break;
        }
    }
    return i;
}

void SnackCart::adjustMealCost(string name, float cost) {
    int i = findMeal(name);
    if (i < count) { // found a matching name
        meal[i].setCost(cost);
    } else {
        cout << "Error: invalid meal name for this cart" << endl;
    }
}

void SnackCart::adjustMealRating(string name, RatingType rating) {
    int i = findMeal(name);
    if (i < count) { // found a matching name
        meal[i].setRating(rating);
    } else {
        cout << "Error: invalid meal name for this cart" << endl;
    }
}


string SnackCart::getLocation() {
    return location;
}

int SnackCart::mealCount() {
    return count;
}

int SnackCart::getMealNames(string names[]) {
    for (int i = 0; i < count; ++i) {
        names[i] = meal[i].getName();
    }
    return count;
}

float SnackCart::getMealCost(string name) {
    return meal[findMeal(name)].getCost();
}

string SnackCart::getMealRatingForName(string name) {
    return meal[findMeal(name)].getRatingStr();
}

string SnackCart::cheapestMeal() {
    if (count == 0) {
        return "Unknown";
    }
    float min = meal[0].getCost();
    int minIndex = 0;
    int i = 1;
    while (i < count) {
        float value = meal[i].getCost();
        if (value < min) {
            min = value;
            minIndex = i;
        }
        ++i;
    }

    return meal[minIndex].getName();
}

string SnackCart::getRatedMeal(string ratingStr) {
    string result = "Unknown";
    for (int i = 0; i < count; ++i) {
        if (ratingStr == meal[i].getRatingStr()) {
            result = meal[i].getName();
            break;
        }
    }
    return result;
}

string SnackCart::mostPopularMeal() {
    // of the highest rated meals, find one with the cheapest cost 

    // find highest rating
    RatingType maxRating = UNKNOWN;
    for (int i = 0; i < count; ++i) {
        RatingType value = meal[i].getRating();
        if (value > maxRating) {
            maxRating = value;
        }
    }

    // find indices of highest rated meals
	int *bestMeals = new int[size];
    int j = 0;
    for (int i = 0; i < count; ++i) {
        if (meal[i].getRating() == maxRating) {
            bestMeals[j++] = i;
        }
    }

    // find best meal with best price of the highest rated meals
    float minCost = meal[bestMeals[0]].getCost();
    int bestMeal = 0;
    for (int i = 1; i < j; ++i) {
        float cost = meal[bestMeals[i]].getCost();
        if (cost < minCost) {
            minCost = cost;
            bestMeal = i;
        }
    }
    return meal[bestMeals[bestMeal]].getName();
	delete [] bestMeals;

}

void SnackCart::displayCartDetails() {
    cout << "Owner: " << owner << endl
        << "Where: " << location << endl;
   cout << "Offers " << count << " different meals" << endl;

   
}

SnackCart::~SnackCart()
{
	if (meals != NULL) {
		delete [] meals;
	}
}

#endif[/code]

[jsmith]

You've already implemented polymorphism via derived classes and virtual functions, so I don't understand
the question.

[Just looking at your code, though, some of what you've done does not make sense.]

[nikman]

the thing is in my main function i have not created a snackcart object as a pointer. it have created it as a vector. does vector have its own destructor? and which part of the code doesnt make sense? i think the *meals is not required and neither is the destructor. is that it?

[jsmith]

vector<> has its own destructor that runs the destructor of all contained elements.


Well, for example, the base class Eatery has a string owner member, but the getter and setter
for that member is pure virtual. And Eatery has a Meal* and a size (an array?), yet all the
derived classes have vectors of Meals. Do the derived classes need both their own vector of
Meals AND an inherited array of Meals?

[nikman]

I get what you mean. I have changed my code accordingly. But without the virtual functions and the meals* is this program still using dynamic objects?

[jsmith]

It's still using derivation, but not really polymorphism.

[nikman]

ok thank you :)