Need help in C++ classes

Quecumber256

Good morning, I need help in designing a class in C++. For experimental purposes I started with something simple. // Header File Planets.h Declares class Planets. class Planets { public: double Mercury; private: double weight; }; //Implementation file Planets.cpp implements the member //functions of Class Planets. #include "stdafx.h" #include "Planets.h" double Planets::Mercury // Pre: Earth weight. // Post: Earth weight times the gravitation constant // of Mercury - 0.4155. { return wgh * 0.4155; } // MT_Planets.cpp : main project file. #include "stdafx.h" #include <iostream> #include "Planets.h" using namespace std; int main() { double iWgh = 235.6; double MyWgh; MyWgh = Planets.Mercury(iWgh); cout << "My weight on Mercury is: " << MyWgh << endl; system("pause"); return 0; } When I try to compile the project I get the following error: Error 1 error C2063: 'Planets::Mercury' : not a function c:\Documents and Settings\Mark McCumber\My Documents\Visual Studio 2005\Projects\Visual C++\MT_Planets\MT_Planets\Planets.cpp 10 Can someone explain to me what I'm doing wrong? Quecumber256

Rajesh R Subramanian

Quecumber256 wrote:

class Planets { public: double Mercury; double Mercury();

Quecumber256 wrote:

double Planets::Mercury double Planets::Mercury() { return wgh * 0.4155; }

Mercury - It is a function? Then you missed the ()

Quecumber256 wrote:

system("pause");

You MUST not do this. This is bad in several ways. Something like a getch(); or std::cin.get(); will do instead.

It is a crappy thing, but it's life -^ Carlo Pallini

Quecumber256

Rajesh, Thank you for the reply, but I'm still getting a problem. I'm trying to reprogram my brain to use OOP instead of procedural programming. The problem is simple in concept. Take a person's Earth weight and calcultate their weight on the other planets of our Solar system. The trick here is it has got to be done using classes and constructors. For example: MyWgh = Planets.Mercury(235.5) would give me their weight on the planet Mercury. According to the instructions the default constructor should return the weight enter for Earth. Can you help me grasp this concept? Quecumber256

Iain Clarke Warrior Programmer

The idea of the assignment will be to teach you polymorphism. I'm assuming you'll want a base class of CPlanet, with more specialised inheriting classes which over-ride the member functions of CPlanet. So, you would have CEarth, and CMercury both inheriting from CPlanet, and each overriding (eg) GetWeight (double dMass), and GetDistanceFromSun (), and so on. // slightly advanced bit here As there is no need for the CPlanet class to even have an implementation of GetDistanceFromSun, you could even leave it as a pure virtual member function, forcing any inheriting classes to implement it. // end of slighty advanced bit. You would end up with:

CEarth earth;
CMercury mercury;
double weight;

weight = earth.GetWeight (100);
cout << "100 kg on earth is : " << weight << endl;
weight = mercury.GetWeight (100);
cout << "100 kg on mercury is : " << weight << endl;

and could even end up with:

CPlanet \*planet = GetNthPlanet (5);
double weight;
weight = planet->GetWeight (100);
cout << "100 kg on 5th planet is : " << weight << endl;

delete planet;

CPlanet *GetNthPlanet (int n)
{
switch (n)
{
case 1: return new CMercury;
case 2: return new CVenus;
// and so on
case 9:
if ( (rand() %100) < 10)
return CPluto;
else
return CPlanetoid;
}
return NULL; // FAIL!
}

I'm hesitant to write much more, as I don't want to spoonfeed you - if you don't struggle a bit, you don't learn. Iain.

Quecumber256

Iain, Thanks, but this gets away from my initial problem; defining the Planets class for use. Quecumber256

CPallini

Something similar to:

#include <iostream>
using namespace std;

class Planet
{
private:
double _dFactor;

public:
Planet(double dFactor = 1.0) : _dFactor(dFactor) {}

double localWeight(double dWeightOnEarth)
{
return dWeightOnEarth * _dFactor;
}
};
void main()
{
Planet planetEarth, planetMercury(.38);
double dYourWeight = 235.6;

cout << "If your weight on Earth is " << planetEarth.localWeight(dYourWeight) << endl;
cout << "then weight on Mercury is " << planetMercury.localWeight(dYourWeight) << endl;
}

? :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

Quecumber256

Thanks, this example helped me with my problem. Quecumber256

CPallini

I'm glad of. BTW did you notice .38 instead of 0.4155? :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

Quecumber256

Yes I did, but I used 0.4155 because that was the number provided in the text. I bet the number you gave me was the most accurate one. Quecumber256

CPallini

Well, actually your number is accurate, expressing the wrong physical quantity. :-D

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]