Hi. I'm new to this whole stuff, and I'm trying to make my own class to solve a range of maths problems. The class, unruprisingly, is called numbers.

There are 3 files which are causing me problems: numbers.h, problem27.cpp, numbers.cpp. I'll include the sources below. My problem is the error message, when I try to execute problem27.cpp.

**/home/bumcheekcity/Desktop/C++/euler/problem27/src/problem27.cpp:13: undefined reference to `numbers::numbers()'**

Line 13, btw, is the line **numbers num;** in problem27.cpp. What am I doing wrong? I'm using "Problem Solving, Abstraction and Design in C++" by Friedman to help me learn, and programming on Ubuntu Linux, using KDevelop. Any assistance will be much appreciated.

**numbers.h**

Code:

//These lines are used to make sure that there are no problems with multiple definitions.
#ifndef NUMBERS_H_
#define NUMBERS_H_
class numbers
{
public :
//Constructors
numbers();
numbers(float);
//Obvious ones
void decrement();
void increment();
bool is_int();
bool is_prime();
void set_value(float);
float show_value();
private:
float value;
};
#endif

**problem27.cpp**

Code:

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <iostream>
#include <cstdlib>
#include "numbers.h"
using namespace std;
int main(int argc, char *argv[])
{
numbers num;
cout << "is the value";
//num.increment();
cout << "is the new value";
return EXIT_SUCCESS;
}

**numbers.cpp**

Code:

#include <iostream>
#include <maths>
#include "numbers.h"
//Here are the two constructors, one with, one without argument.
numbers::numbers()
{
value = 0;
}
numbers::numbers(float initial_value)
{
value = initial_value;
}
//End constructors.
void decrement()
{
value--;
}
void increment()
{
value++;
}
bool is_int()
{
}
bool is_prime()
{
//Obvious
}
void set_value(float new_value)
{
value = new_value;
}
float show_value()
{
return value;
}