ich sollte diese klasse implementieren:

namespace test_1
{
    class statistician
    {
    public:
        // CONSTRUCTOR
        statistician( );
        // MODIFICATION MEMBER FUNCTIONS
        void next(double r);
        void reset( );
        // CONSTANT MEMBER FUNCTIONS
        int length( ) const;
        double sum( ) const;
        double mean( ) const;
        double minimum( ) const;
        double maximum( ) const;
        // FRIEND FUNCTIONS
        friend statistician operator +
            (const statistician & s1, const statistician & s2);
        friend statistician operator *
            (double scale, const statistician & s);
    private:
        int count;       // How many numbers in the sequence
        double total;    // The sum of all the numbers in the sequence
        double tinyest;  // The smallest number in the sequence
        double largest;  // The largest number in the sequence
    };

    // NON-MEMBER functions for the statistician class
    bool operator ==(const statistician& s1, const statistician& s2);
}

Nur ist mir nicht ganz klar, was der unterschied der friend und non-member function (operator ==) zu den normalen member function in diesem header file ist bzw. wie ich diese im implmentation file dann definieren muss...?

kann mir hier jemand weiterhelfen?

lg matti

class foo {
  int i;
public:
  friend int bar(foo const &a);
};

int bar(foo const &a) {
  return a.i;
}

Also mein header-file

#ifndef STATS_H     // Prevent duplicate definition
#define STATS_H
#include <iostream>

namespace test_1
{
    class statistician
    {
    public:
        // CONSTRUCTOR
        statistician( );
        // MODIFICATION MEMBER FUNCTIONS
        void next(double r);
        void reset( );
        // CONSTANT MEMBER FUNCTIONS
        int length( ) const;
        double sum( ) const;
        double mean( ) const;
        double minimum( ) const;
        double maximum( ) const;
        // FRIEND FUNCTIONS
        friend statistician operator +
            (const statistician & s1, const statistician & s2);
        friend statistician operator *
            (double scale, const statistician & s);
    private:
        int count;       // How many numbers in the sequence
        double total;    // The sum of all the numbers in the sequence
        double tinyest;  // The smallest number in the sequence
        double largest;  // The largest number in the sequence
    };

    // NON-MEMBER functions for the statistician class
    bool operator ==(const statistician& s1, const statistician& s2);
}

#endif

Hier die Implementation aber nur halt mal der Rumpf, da ich nur mal sehen möchte, ob das testfile überhaupt korrekt startet:

#include "stats.h"

using namespace test_1;

statistician::statistician()
{

}

void statistician::next(double r)
{

}

int statistician::length() const
{
    return 0;
}

double statistician::sum() const
{
    return 0;
}

double statistician::mean() const
{
    return 0;
}

double statistician::minimum() const
{
    return 0;
}

double statistician::maximum() const
{
    return 0;
}

bool operator ==(const statistician& s1, const statistician& s2)
{
	return true;
}

statistician operator + (const statistician & s1, const statistician & s2)
{
	return s1;
}

statistician operator * (double scale, const statistician & s)
{
	return s;
}

Und hier das Testfile:

#include <cctype>    // Provides toupper
#include <iomanip>   // Provides setw to set the width of an output
#include <iostream>  // Provides cout, cin
#include <cstdlib>   // Provides EXIT_SUCCESS
#include "stats.h"

using namespace test_1;
using namespace std;

// PROTOTYPES of functions used in this test program:
void print_menu( );

char get_user_command( );

double get_number( );

void print_values(const statistician& s);

int main( )
{
    statistician s1, s2, s3;  // Three statisticians for us to play with
    char choice;              // A command character entered by the user
    double x;                 // Value for multiplication x*s1

    cout << "Three statisticians s1, s2, and s3 are ready to test." << endl;

    do
    {
        cout << endl;
        print_menu( );
        choice = toupper(get_user_command( ));
        switch (choice)
        {
            case 'R': cout << "Which one should I reset (1, 2, 3) " << endl;
                      choice = get_user_command( );
                      switch (choice)
                      {
			  case '1': s1.reset( );
                                    break;
			  case '2': s2.reset( );
                                    break;
			  case '3': s3.reset( );
                                    break;
                      }
                      cout << "Reset activated for s" << choice << "." << endl;
                      break;
            case '1': s1.next(get_number( ));
                      break;
            case '2': s2.next(get_number( ));
                      break;
            case '3': s3.next(get_number( ));
                      break;
            case 'T': cout << "The values are given in this table:" << endl;
                      cout << "        LENGTH       SUM"
                           << "   MINIMUM      MEAN   MAXIMUM" << endl;
                      cout << "  s1";
                      print_values(s1);
                      cout << "  s2";
                      print_values(s2);
                      cout << "  s3";
                      print_values(s3);
                      break;
            case 'E': if (s1 == s2)
                          cout << "s1 and s2 are equal." << endl;
                      else
                          cout << "s1 and s2 are not equal." << endl;
                      break;
            case '+': s3 = s1 + s2;
                      cout << "s3 has been set to s1 + s2" << endl;
                      break;
            case '*': cout << "Please type a value for x: ";
                      cin >> x;
                      s3 = x * s1;
                      cout << "s3 has been set to " << x << " * s1" << endl;
		      break;
            case 'Q': cout << "Ridicule is the best test of truth." << endl;
                      break;
            default: cout << choice << " is invalid. Sorry." << endl;
        }
    }
    while ((choice != 'Q'));

    return EXIT_SUCCESS;

}

void print_menu( )
{
    cout << endl;
    cout << "The following choices are available: " << endl;
    cout << " R  Activate one of the reset( ) functions" << endl;
    cout << " 1  Add a new number to the 1st statistician s1" << endl;
    cout << " 2  Add a new number to the 2nd statistician s2" << endl;
    cout << " 3  Add a new number to the 3rd statistician s3" << endl;
    cout << " T  Print a table of values from the statisticians" << endl;
    cout << " E  Test whether s1 == s2" << endl;
    cout << " +  Set the third statistician s3 equal to s1 + s2" << endl;
    cout << " *  Set the third statistician s3 equal to x*s1" << endl;
    cout << " Q  Quit this test program" << endl;
}

char get_user_command( )
// Library facilties used: iostream.h
{
    char command;

    cout << "Enter choice: ";
    cin >> command; 

    return command;
}

double get_number( )
// Library facilties used: iostream.h
{
    double result;

    cout << "Please enter the next real number for the sequence: ";
    cin  >> result;
    cout << result << " has been read." << endl;
    return result;
}

void print_values(const statistician& s)
// Library facilties used: iostream.h
{
    cout << setw(10) << s.length( );
    cout << setw(10) << s.sum( );
    if (s.length( ) != 0)
    {
        cout << setw(10) << s.minimum( );
        cout << setw(10) << s.mean( );
        cout << setw(10) << s.maximum( );
    }
    else
        cout << "      none      none      none";
    cout << endl;
}

Nur wenn ich dann das testfile ausführe kommen folgende Fehler:

------ Build started: Project: Assignment1, Configuration: Debug Win32 ------
Compiling...
stattest.cpp
Linking...
stattest.obj : error LNK2019: unresolved external symbol "class main_savitch_2C::statistician __cdecl main_savitch_2C::operator*(double,class main_savitch_2C::statistician const &)" (??Dmain_savitch_2C@@YA?AVstatistician@0@NABV10@@Z) referenced in function _main
stattest.obj : error LNK2019: unresolved external symbol "class main_savitch_2C::statistician __cdecl main_savitch_2C::operator+(class main_savitch_2C::statistician const &,class main_savitch_2C::statistician const &)" (??Hmain_savitch_2C@@YA?AVstatistician@0@ABV10@0@Z) referenced in function _main
stattest.obj : error LNK2019: unresolved external symbol "bool __cdecl main_savitch_2C::operator==(class main_savitch_2C::statistician const &,class main_savitch_2C::statistician const &)" (??8main_savitch_2C@@YA_NABVstatistician@0@0@Z) referenced in function _main
stattest.obj : error LNK2019: unresolved external symbol "public: void __thiscall main_savitch_2C::statistician::reset(void)" (?reset@statistician@main_savitch_2C@@QAEXXZ) referenced in function _main
C:\Dokumente und Einstellungen\matti\Eigene Dateien\Visual Studio 2005\Projects\Assignment1\Debug\Assignment1.exe : fatal error LNK1120: 4 unresolved externals
Build log was saved at "file://c:\Dokumente und Einstellungen\matti\Eigene Dateien\Visual Studio 2005\Projects\Assignment1\Assignment1\Debug\BuildLog.htm"
Assignment1 - 5 error(s), 0 warning(s)

Weiß hier irgendjemand weiter??

matti

------ Build started: Project: Assignment1, Configuration: Debug Win32 ------
Compiling...
statsimpl.cpp
Linking...
stattest.obj : error LNK2019: unresolved external symbol "class main_savitch_2C::statistician __cdecl main_savitch_2C::operator*(double,class main_savitch_2C::statistician const &)" (??Dmain_savitch_2C@@YA?AVstatistician@0@NABV10@@Z) referenced in function _main
stattest.obj : error LNK2019: unresolved external symbol "class main_savitch_2C::statistician __cdecl main_savitch_2C::operator+(class main_savitch_2C::statistician const &,class main_savitch_2C::statistician const &)" (??Hmain_savitch_2C@@YA?AVstatistician@0@ABV10@0@Z) referenced in function _main
stattest.obj : error LNK2019: unresolved external symbol "bool __cdecl main_savitch_2C::operator==(class main_savitch_2C::statistician const &,class main_savitch_2C::statistician const &)" (??8main_savitch_2C@@YA_NABVstatistician@0@0@Z) referenced in function _main
C:\Dokumente und Einstellungen\matti\Eigene Dateien\Visual Studio 2005\Projects\Assignment1\Debug\Assignment1.exe : fatal error LNK1120: 3 unresolved externals
Build log was saved at "file://c:\Dokumente und Einstellungen\matti\Eigene Dateien\Visual Studio 2005\Projects\Assignment1\Assignment1\Debug\BuildLog.htm"
Assignment1 - 4 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========