"undefined reference" in my Class

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;
}

add numbers.cpp to the project.
or compile like this

Code:

g++ problem27.cpp numbers.cpp -o problem27

Kurt

> void decrement()
Include the class:: scope resolution bit, to make the functions part of the class.

Something along the lines of:

Code:

include "numbers.cpp"

????

Originally Posted by bumcheekcity

Something along the lines of:

Code:

include "numbers.cpp"

????

No. What salem meant was that decrement() and increment() ... are part of the class.
you have to implement them like

Code:

void numbers::decrement() {
	value--;
}

Kurt

Thanks for the help. My numbers.cpp page now looks as shown, but I have a problem with calling a function within a class. I can do it in PHP, by calling $this->functionname. How is it done in C++? I gett he following errors.

/home/bumcheekcity/Desktop/C++/euler/problem27/src/numbers.cpp:39: error: no matching function for call to ‘numbers::is_int(double)’
/home/bumcheekcity/Desktop/C++/euler/problem27/src/numbers.cpp:26: note: candidates are: bool numbers::is_int()


The relevent lines are the huge if statement in the is_prime() function, and the declaration:
bool numbers::is_int() (Line 26)
if ((!is_int(value)) || (value < 2) || (is_int(sqrt(value))) || ((int(value) &#37; 2 == 0) && (value != 2))) (Line 39)

Code:

#include <iostream>
#include <math.h>
#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 numbers::decrement()
{
	value--;
}

void numbers::increment()
{
	value++;
}

bool numbers::is_int()
{
	if (int(value) == value)
	{
		return true;
	} else {
		return false;
	}
}

bool numbers::is_prime()
{
	//A non-integer can't be a prime, neither can one that is less than 2, is a perfect square, or that divides by 2 and isn't two.
	if ((!is_int(value)) || (value < 2) || (is_int(sqrt(value))) || ((int(value) % 2 == 0) && (value != 2)))
		return false;
	
	//2 is a prime.
	if (value == 2)
		return true;

	//Else, from 3, loop up the odd numbers until you get to the square root.
	int count;
	for (count = 3; count < sqrt(value); count = count + 2)
	{
		if ((int(value) % count) == 0)
			return false;
	}
	return true;
}

void numbers::set_value(float new_value)
{
	value = new_value;
}

float numbers::show_value()
{
	return value;
}

can do it in PHP, by calling $this->functionname.

something like this can be done in c++ as well but is rarely necessary ( only if you pass arguments with the same name as members ).
it would be

Code:

this->func();

value is a member of the class so the statement should look like this

Code:

if ((!is_int()) || (value < 2) || (is_int(sqrt())) || ((int(value) % 2 == 0) && (value != 2)))

Kurt

The sqrt() is giving me problems, so I just dropped that. Anyway, it's working brilliantly now. Thanks very much

Originally Posted by bumcheekcity

The sqrt() is giving me problems, so I just dropped that. Anyway, it's working brilliantly now. Thanks very much

You have to link to the math library.

Code:

g++ problem27.cpp numbers.cpp -lm -o problem27

I thought sqrt() was a member of the numbers class as well.

Code:

if ((!is_int()) || (value < 2) || (is_int(sqrt(value))) || ((int(value) % 2 == 0) && (value != 2)))

Kurt