Thread: understanding user-defined classes

I'm trying to learn about "user defined classes" and don't understand what they're for. Once I see a project compile it seems to click with me so I typed up the source file and matching "user defined class definition" that is in the user-defined classes chapter of my book. This file is a "counter class" of some sort. I put both the .cpp and .h files into one project and it didn't work. I was hoping to see what the advantage of a user-defined class was by seeing it work, but no luck. I tried another set that deals with "cube" I found on the net and it didn't work as well, so I must be missing something. As far as what I did to get these results: I added the header file by clicking on "add new item" under the tree. all that is there is a counter.h file and in the same project is a .cpp file which is included below. I have also included the info I found on the net; it is in the second half of this post.

Code:

#ifndef COUNTER_H	
#define COUNTER_H

class counter
{
public:

	counter();
	counter(int);

	void increment();

	void decrement();
	void setCount(int);

	void setMaxValue(int);

	int getCount() const;

	int  getMaxValue() const;

private:

	int count;
	int maxValue;

};

#endif // COUNTER_H

Code:

#include <iostream>
#include "header1.h"
using namespace std;

int main ()
{

	counter c1;

	counter c2(10);

	c1.setCount(50);
	c1.decrement();
	c1.decrement();
	c1.increment();
	cout << "Final value of c1 is " << c1.getCount() << endl;

	c2.increment();
	c2.increment();
	c2.decrement();
	cout << "Final value of c2 is " << c2.getCount() << endl;

	return 0;

}

Here are the errors that come up:

1>------ Build started: Project: classPractice, Configuration: Debug Win32 ------
1>Compiling...
1>classPractice.cpp
1>Compiling manifest to resources...
1>Linking...
1>classPractice.obj : error LNK2019: unresolved external symbol "public: int __thiscall counter::getCount(void)const " (?getCount@counter@@QBEHXZ) referenced in function _main
1>classPractice.obj : error LNK2019: unresolved external symbol "public: void __thiscall counter::increment(void)" (?increment@counter@@QAEXXZ) referenced in function _main
1>classPractice.obj : error LNK2019: unresolved external symbol "public: void __thiscall counter::decrement(void)" (?decrement@counter@@QAEXXZ) referenced in function _main
1>classPractice.obj : error LNK2019: unresolved external symbol "public: void __thiscall counter::setCount(int)" (?setCount@counter@@QAEXH@Z) referenced in function _main
1>classPractice.obj : error LNK2019: unresolved external symbol "public: __thiscall counter::counter(int)" (??0counter@@QAE@H@Z) referenced in function _main
1>classPractice.obj : error LNK2019: unresolved external symbol "public: __thiscall counter::counter(void)" (??0counter@@QAE@XZ) referenced in function _main


==================================================
here is the info for the cube project:

Code:

#ifndef CUBE_H#define CUBE_Hclass Cube{public:	Cube();	~Cube();	
void setSide(double s);	
double getSide();	
double Area();	
double Volume();	
void Properties();private:	double Side;
};#endif

Code:

#include <iostream>
#include "cube.h"

Cube::Cube(){}Cube::~Cube(){}

void Cube::setSide(double s)
{	
Side = s <= 0 ? 1 : s;
}

double Cube::getSide()

{	
	return Side;
}
double Cube::Area()
{
	
return 6 * Side * Side;

}double Cube::Volume()
{	
return Side * Side * Side;
}void Cube::Properties()
{	
cout << "Characteristics of this cube";	
cout << "\nSide   = " << getSide();	
cout << "\nArea   = " << Area();	
cout << "\nVolume = " << Volume() << "\n\n";
}

you never implemented those functions.

you have defined the functions in the class definition in your header file, you have called on the the functions in main() to use them, but there are no other instructions anywhere that actually code what the functions calls 'do'

i.e you would have more blocks of code in another source file (counters.cpp??), or in main if you like for a small project,
an example like >

Code:

void counter::decrement()
}
     count --;
}

now your member variable 'count' is decremented by the member function 'decrement()' when it is called in main(), this is the implementation of your function.

the example in the book doesn't have that. I looked at a different class example in the book and it has a few .cpp files. one is called a driver function and the other is called an implementation file; both have to do with a fraction class and has a fraction class definition. does this mean my tree will have 2 .cpp files and one header file? All of the programs I have done so far have just one .cpp file with no add'l header file.