"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:

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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:

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include "numbers.cpp"

---

????

Quote:

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Originally Posted by bumcheekcity

Something along the lines of:

Code:

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include "numbers.cpp"

---

????

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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;
}

---

Quote:

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

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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:

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this->func();

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

Code:

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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 :D

Quote:

---

Originally Posted by bumcheekcity

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

---

You have to link to the math library.

Code:

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

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

Code:

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

---

Kurt