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Multiple constructors ? (exercise from Deitel's C++ Book)

andyw27
andyw27 asked
on
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Last Modified: 2012-08-14

Hi,

I'm a novice working through the Deitel, C++ How to Program book.

I just finished reviewing the chapter on classes and I'm stuck on the following exercise:

 (Modifying Class GradeBook) Modify class GradeBook (Fig. 3.11–Fig. 3.12) as follows:
 a) Include a second string data member that represents the course instructor’s name.
 b) Provide a set function to change the instructor’s name and a get function to retrieve it.
 c) Modify the constructor to specify two parameters—one for the course name and one for the instructor’s name.
 d) Modify member function displayMessage such that it first outputs the welcome message and course name, then outputs “This course is presented by:” followed by the instructor’s name.
 Use your modified class in a test program that demonstrates the class’s new capabilities.
-----------------------------------------------------------------------------------------------------------------

I had success in (a) (b) but (c) is not working as expected.  I think its a syntax error in the constructor, any how here is the code I have:

gradebook.h

#include <string>
using std::string;

// GradeBook class definition
class GradeBook
{
public:
      GradeBook( string ); // constructor that initializes courseName
      void setCourseName( string ); // function that sets the course name
      string getCourseName(); // function that gets the course name
      void displayMessage(); // function that displays a welcome message

      void setInstructorName( string );
      string getInstructorName();

private:
      string courseName; // course name for this gradebook
      string instructorName;
};


gradebook.cpp

#include <iostream>
using std::cout;
using std::endl;

#include "gradebook.h"

// constructor initializes courseName with string supplied as argument
GradeBook::GradeBook( string name )
{
      setCourseName( name );
      setInstructorName (name );

}

// function to set the course name
void GradeBook::setCourseName( string name )
{
      if (name.length() <= 5)
            courseName = name;

      if (name.length() > 5)
      {
            courseName = name.substr(0, 5);

            cout << "Name \ " << name << "\ exceeds maximum length (5).\n"
             << "Limiting courseName to first 5 characters.\n" << endl;
      } //end if statement
}

// function to get the course name
string GradeBook::getCourseName()
{
      return courseName;
}

//display a welcome message to the gradebook user
void GradeBook::displayMessage()
{
      // call getCourseName to get the courseName
      cout << "Welcome to the grade book for\n" << getCourseName()
            << "!" << endl;
}

void GradeBook::setInstructorName( string name )
{
      instructorName = name;
}

string GradeBook::getInstructorName()
{
      return instructorName;
}

lesson03.cpp

#include <iostream>
using std::cout;
using std::endl;

#include "GradeBook.h"

int main()
{
      GradeBook gradebook1( "12345" );
      GradeBook gradebook2( "654321" "bob" );


      cout << "gradebook1 created for course: " << gradebook1.getCourseName()
            << "\ngradebook2 created for course: " << gradebook2.getCourseName()
            << " and the instructor is called " << gradebook2.getInstructorName()
            << endl;

      return 0;
}

Thanks for any guidance.
Comment
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Senior Software Engineer
Commented:
Hi andyw27,
>  GradeBook gradebook2( "654321" "bob" );

The above line should have a comma between the two arguments:
GradeBook gradebook2( "654321", "bob" );


David Maisonave (Axter)
Cheers!

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AxterSenior Software Engineer

Commented:
andyw27,
> GradeBook::GradeBook( string name )

The above constructor needs to be given two arguments.
GradeBook::GradeBook( string CourseName, string InstructorName ) //Always give a well descriptive name for your arguments.  Name really doesn't say much about an argument.


David Maisonave (Axter)
AxterSenior Software Engineer

Commented:
andyw27,
> class GradeBook
> {
> public:
>      GradeBook( string );

Don't forget to also change your head (class declaration.
class GradeBook
{
public:
     GradeBook(  string CourseName, string InstructorName );

Argument names are not required in function declaration, but it's good practice to always give argument names, because it's easier for other developers to determine what type of argument they need to pass.    

David Maisonave (Axter)
AxterSenior Software Engineer

Commented:
andyw27,
> using std::string;

You should avoid putting using clause in a header.
Instead, use fully qualified names for all std objects in the header.

David Maisonave (Axter)

Author

Commented:

David - thanks for response.

I changed as suggested, still getting an error.  What should the variables name by for the get and set for instructor, at the moment they are:

void GradeBook::setInstructorName( string iname )
{
      instructorName = iname;
}

string GradeBook::getInstructorName()
{
      return instructorName;
}

-------------------------

// constructor initializes courseName with string supplied as argument
GradeBook::GradeBook( string name, string iname )
{
      setCourseName( name );
      setInstructorName (iname );

}

Author

Commented:

ah, you third post solved the problem I was getting.
AxterSenior Software Engineer

Commented:
>>What should the variables name by for the get and set for instructor, at the moment they are:
If you made your member variables have an m_ prefix (as in hungarian notation), then you could do the following:

void GradeBook::setInstructorName( string instructorName)
{
     m_instructorName = instructorName;
}

>>I changed as suggested, still getting an error.
Please post the exact error you're getting.

Author

Commented:

One other thing I noticed.

If I have a constructor that contains two parameters, in this case:
      setCourseName( name );
      setInstructorName (iname );

When I create an object do I have to always set both of these, for example I tried the following:

      cout << "gradebook1 created for course: " << gradebook1.getCourseName()
            << "\ngradebook2 created for course: " << gradebook2.getCourseName()
            << " and the instructor is called " << gradebook2.getInstructorName()

I didn't want to define a value for instructorName for the object gradebook1?
You can have a default value for a constructor parameter just like any function.

class GradeBook {
    const string courseName;
    const string instructorName;
public:
    GradeBook(const string& courseName,const string& instructorName = "");
    // ..
};

GradeBook::GradeBook(const string& courseName,const string& instructorName) : courseName(courseName),instructorName(instructorName)
{
}

int main()
{
    GradeBook latin("Latin","Mr Chips");
    GradeBook biology("Biology");
}
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