Constructor problem

[Chiller]

Re: Constructor problem

Thanks Mark,

I'm trying to write a class (Distance.h file and a Distance.cpp) file that
will accept two arguments, one being a value and the other being a unit (ie
km, m, or cm). I'm trying to write the class to include overloads for ==,
!=, <, <=, > and >= which will return a boolean value. As well as overloads
of + and -. Obviously the overloads will only work on multimple instances,
ie when I enter more than a single value.

What I've written so far is included within this thread.

Thanks

[Chiller]

Re: Constructor problem

Thanks Mark,

I'm trying to write a class (Distance.h file and a Distance.cpp) file that
will accept two arguments, one being a value and the other being a unit (ie
km, m, or cm). I'm trying to write the class to include overloads for ==,
!=, <, <=, > and >= which will return a boolean value. As well as overloads
of + and -. Obviously the overloads will only work on multimple instances,
ie when I enter more than a single value.

What I've written so far is included within this thread.

Thanks

[Chiller]

Re: Constructor problem

Thanks John,

I obviously need to take a break for a while.

Regards

[Chiller]

Re: Constructor problem

Thanks John,

I obviously need to take a break for a while.

Regards

[Chiller]

Re: Constructor problem

John,

I've taken your suggestion and included enum; however, when I output the
stored values to screen, all the values are int values. What I'm trying to
do is to be able to enter a value and unit and be able to output the same
value and unit. ie, if I input Distance a (5, m) I'd like to be able to
output the same. Once I've got this working my next step will be to
implement some overloaded operators to perform addition, subtraction etc on
any objects created by the class.

I've included what I've done so far below. If you compile and execute the
program you'll see what I mean by the output being in the wrong format.I'd
appreciate any advice on this.

Thanks


Distance.h

*************** *************** ******
#ifndef DISTANCE_H

#define DISTANCE_H

#include <iostream>

using namespace std;

class Distance

{

public :

Distance (int, int) ; // constructor - takes int values

Distance (int) ; // constructor - takes int value

Distance (void) ; // default - zero

//access member functions

int number (void) const;

int measure (void) const;


private :

int nu ; // the value

int me ; // the unit of measure (m)

} ;

// provide an overload of "<<" for easy display

ostream& operator<< (ostream&, const Distance&);

#endif



Distance.cpp as follows:

*************** *************** ***********

#include "Distance.h "

#include <iostream>

using namespace std;

/*-------------------------------------------------------*\

| implementation of member functions |

\*-------------------------------------------------------*/

// constructor

Distance :: Distance (int n, int m) : nu(n), me(m) {}

Distance :: Distance (int n) : nu(n) {}

Distance :: Distance (void) : nu(0) {}



enum

{

m,

km,

};



// access functions

int Distance :: number (void) const

{

return nu;

}

int Distance :: measure (void) const

{

return me;

}

// provide an overload of "<<" for easy display

ostream& operator<< (ostream& out, const Distance& d)

{

out << "(" << d.number() << "," << d.measure() << ")" ;

return out;

}

/*-------------------------------------------------------*\

| test driver for the Distance class |

\*-------------------------------------------------------*/

#ifdef TEST_DISTANCE // .... Distance class .... test driver

int main (void)

{

// create test input

Distance a = Distance (6);

Distance b (4);

Distance c (2);

Distance d;

Distance e (5, m);


cout << a << endl << b << endl << c << endl << d << endl << e << endl;



cin.ignore();

return 0; // normal termination

}

#endif

[Chiller]

Re: Constructor problem

John,

I've taken your suggestion and included enum; however, when I output the
stored values to screen, all the values are int values. What I'm trying to
do is to be able to enter a value and unit and be able to output the same
value and unit. ie, if I input Distance a (5, m) I'd like to be able to
output the same. Once I've got this working my next step will be to
implement some overloaded operators to perform addition, subtraction etc on
any objects created by the class.

I've included what I've done so far below. If you compile and execute the
program you'll see what I mean by the output being in the wrong format.I'd
appreciate any advice on this.

Thanks


Distance.h

*************** *************** ******
#ifndef DISTANCE_H

#define DISTANCE_H

#include <iostream>

using namespace std;

class Distance

{

public :

Distance (int, int) ; // constructor - takes int values

Distance (int) ; // constructor - takes int value

Distance (void) ; // default - zero

//access member functions

int number (void) const;

int measure (void) const;


private :

int nu ; // the value

int me ; // the unit of measure (m)

} ;

// provide an overload of "<<" for easy display

ostream& operator<< (ostream&, const Distance&);

#endif



Distance.cpp as follows:

*************** *************** ***********

#include "Distance.h "

#include <iostream>

using namespace std;

/*-------------------------------------------------------*\

| implementation of member functions |

\*-------------------------------------------------------*/

// constructor

Distance :: Distance (int n, int m) : nu(n), me(m) {}

Distance :: Distance (int n) : nu(n) {}

Distance :: Distance (void) : nu(0) {}



enum

{

m,

km,

};



// access functions

int Distance :: number (void) const

{

return nu;

}

int Distance :: measure (void) const

{

return me;

}

// provide an overload of "<<" for easy display

ostream& operator<< (ostream& out, const Distance& d)

{

out << "(" << d.number() << "," << d.measure() << ")" ;

return out;

}

/*-------------------------------------------------------*\

| test driver for the Distance class |

\*-------------------------------------------------------*/

#ifdef TEST_DISTANCE // .... Distance class .... test driver

int main (void)

{

// create test input

Distance a = Distance (6);

Distance b (4);

Distance c (2);

Distance d;

Distance e (5, m);


cout << a << endl << b << endl << c << endl << d << endl << e << endl;



cin.ignore();

return 0; // normal termination

}

#endif

[SaltPeter]

Re: Constructor problem


"Chiller" <...@...> wrote in message
news:59b0c5bce8 57990952dc322b6 a1458b2@news.te ranews.com...[color=blue]
> Is there a way that I can write the constructor so that it will simply
> accept two variables, ie. when I create an object I can do so by simply
> typing
>
> Distance a = Distance (5, m); or
> Distance a = Distance (5, km); etc
>
> without having to use ' ' or declaring m, km?
>
> Thanks
>[/color]
You need to refine your knowledge of constants.
The arguements provided are not variables. 5 is a constant ( a literal
value). The second arguement can be a std::string or enum but its also a
constant here. You don't have to use the second arguement if you plan on
providing a consistant measurement base (like meters). Personally, i'ld
prefer a constructor with an init list and passing constants by reference:

#include <iostream>
#include <string>

class Distance
{
public:
Distance(const int& r_distance) : meters(r_distan ce) { }
virtual ~Distance() { }
void display() const { std::cout << "distance = " << meters <<
std::endl; }
private:
int meters;
};

int main()
{
Distance dist(5000);
dist.display();
return 0;
}

[SaltPeter]

Re: Constructor problem


"Chiller" <...@...> wrote in message
news:59b0c5bce8 57990952dc322b6 a1458b2@news.te ranews.com...[color=blue]
> Is there a way that I can write the constructor so that it will simply
> accept two variables, ie. when I create an object I can do so by simply
> typing
>
> Distance a = Distance (5, m); or
> Distance a = Distance (5, km); etc
>
> without having to use ' ' or declaring m, km?
>
> Thanks
>[/color]
You need to refine your knowledge of constants.
The arguements provided are not variables. 5 is a constant ( a literal
value). The second arguement can be a std::string or enum but its also a
constant here. You don't have to use the second arguement if you plan on
providing a consistant measurement base (like meters). Personally, i'ld
prefer a constructor with an init list and passing constants by reference:

#include <iostream>
#include <string>

class Distance
{
public:
Distance(const int& r_distance) : meters(r_distan ce) { }
virtual ~Distance() { }
void display() const { std::cout << "distance = " << meters <<
std::endl; }
private:
int meters;
};

int main()
{
Distance dist(5000);
dist.display();
return 0;
}

[John Harrison]

Re: Constructor problem


"Chiller" <...@...> wrote in message
news:63fb2e2141 4512839f2c71f99 5182bf0@news.te ranews.com...[color=blue]
> John,
>
> I've taken your suggestion and included enum; however, when I output the
> stored values to screen, all the values are int values.[/color]

That's because enum's are integer constants.
[color=blue]
> What I'm trying to
> do is to be able to enter a value and unit and be able to output the same
> value and unit. ie, if I input Distance a (5, m) I'd like to be able to
> output the same. Once I've got this working my next step will be to
> implement some overloaded operators to perform addition, subtraction etc[/color]
on[color=blue]
> any objects created by the class.[/color]

There's no way to do that other than the hard way

enum { m, km, };

switch (d.measure())
{
case m:
out << "m";
break;
case km:
out << "km";
break;
}

There's various ways of tarting this up, for instance you could have an
array of unit strings.

enum { m, km, };

const char* const unit_str[] = { "m", "km" };

out << unit_str[d.measure()];

but essentially you have to test the int value of your units and print out
the appropriate string. There is no way of automatically converting the name
of something in your program to a string.

john

[John Harrison]

Re: Constructor problem


"Chiller" <...@...> wrote in message
news:63fb2e2141 4512839f2c71f99 5182bf0@news.te ranews.com...[color=blue]
> John,
>
> I've taken your suggestion and included enum; however, when I output the
> stored values to screen, all the values are int values.[/color]

That's because enum's are integer constants.
[color=blue]
> What I'm trying to
> do is to be able to enter a value and unit and be able to output the same
> value and unit. ie, if I input Distance a (5, m) I'd like to be able to
> output the same. Once I've got this working my next step will be to
> implement some overloaded operators to perform addition, subtraction etc[/color]
on[color=blue]
> any objects created by the class.[/color]

There's no way to do that other than the hard way

enum { m, km, };

switch (d.measure())
{
case m:
out << "m";
break;
case km:
out << "km";
break;
}

There's various ways of tarting this up, for instance you could have an
array of unit strings.

enum { m, km, };

const char* const unit_str[] = { "m", "km" };

out << unit_str[d.measure()];

but essentially you have to test the int value of your units and print out
the appropriate string. There is no way of automatically converting the name
of something in your program to a string.

john

[DaKoadMunky]

Re: Constructor problem

>enum[color=blue]
>{
> m,
> km,
> miles,
>};
>
>etc.
>
>Put that at the top of you program and then change char to int. I.e. you
>constructor becomes
>
>Distance (int, int);
>[/color]

I am curious about your suggestion to change the second parameter from a char
to an int.

Wouldn't it be better to have the enumeration typed and then use that type as
the second parameter? Then the author of the class need not worry that he has
been passed an invalid indicator of unit as the compiler will allow only values
specified in the enumeration to be passed. Of course the caller could cast any
value to the enumerated type, but then they get what they deserve.

Regards.


Brian F. Seaberg
Naperville, Illinois
Delray Beach, Florida

[DaKoadMunky]

Re: Constructor problem

>enum[color=blue]
>{
> m,
> km,
> miles,
>};
>
>etc.
>
>Put that at the top of you program and then change char to int. I.e. you
>constructor becomes
>
>Distance (int, int);
>[/color]

I am curious about your suggestion to change the second parameter from a char
to an int.

Wouldn't it be better to have the enumeration typed and then use that type as
the second parameter? Then the author of the class need not worry that he has
been passed an invalid indicator of unit as the compiler will allow only values
specified in the enumeration to be passed. Of course the caller could cast any
value to the enumerated type, but then they get what they deserve.

Regards.


Brian F. Seaberg
Naperville, Illinois
Delray Beach, Florida

[John Harrison]

Re: Constructor problem

> >[color=blue]
>
> I am curious about your suggestion to change the second parameter from a[/color]
char[color=blue]
> to an int.
>
> Wouldn't it be better to have the enumeration typed and then use that type[/color]
as[color=blue]
> the second parameter? Then the author of the class need not worry that he[/color]
has[color=blue]
> been passed an invalid indicator of unit as the compiler will allow only[/color]
values[color=blue]
> specified in the enumeration to be passed. Of course the caller could[/color]
cast any[color=blue]
> value to the enumerated type, but then they get what they deserve.
>[/color]

Maybe, but I was just trying to introduce one new concept at a time.

Incidentally the OP took my advice but if you read his latest post he's
changed back from an int to a char for some spurious reason.

john

[John Harrison]

Re: Constructor problem

> >[color=blue]
>
> I am curious about your suggestion to change the second parameter from a[/color]
char[color=blue]
> to an int.
>
> Wouldn't it be better to have the enumeration typed and then use that type[/color]
as[color=blue]
> the second parameter? Then the author of the class need not worry that he[/color]
has[color=blue]
> been passed an invalid indicator of unit as the compiler will allow only[/color]
values[color=blue]
> specified in the enumeration to be passed. Of course the caller could[/color]
cast any[color=blue]
> value to the enumerated type, but then they get what they deserve.
>[/color]

Maybe, but I was just trying to introduce one new concept at a time.

Incidentally the OP took my advice but if you read his latest post he's
changed back from an int to a char for some spurious reason.

john