chapter14

Chapter 14 "Reusing Code in C++"

Programming Exercises

1. The Wine class has a string class object member (see Chapter 4 that holds the name of a wine and a Pair object (as discussed in this chapter) of valarray<int> objects (as discussed in this chapter). The first member of each Pair object holds the vintage years, and the second member holds the numbers of bottles owned for the corresponding particular vintage year. For example, the first valarray object of the Pair object might hold the years 1988, 1992,and 1996,and the second valarray object might hold the bottle counts 24, 48, and 144. It may be convenient for Wine to have an int member that stores the number of years. Also some typedefs might be useful to simplify the coding:

   typedef std::valarray<int> ArrayInt;
   typedef Pair<ArrayInt, ArrayInt> PairArray;

   Thus, the PairArray type represents type Pair<std::valarray<int>, std::valarray<int> >. Implement the Wine class by using containment. The class should have a default constructor and at least the following constructors:

   // initialize label to l, number of years to y,
   // vintage years to yr[], bottles to bot[]
   Wine(const char * l, int y, const int yr[], const int bot[]);
   // initialize label to l, number of years to y,
   // create array objects of length y
   Wine(const char * l, int y);

   The Wine class should have a method GetBottles() that, given a Wine object with y years, prompts the user to enter the corresponding number of vintage years and bottle counts. A method Label() should return a reference to the wine name. A method sum() should return the total number of bottles in the second valarray<int> object in the Pair object.

   The program should prompt the user to enter a wine name, the number of elements of the array, and the year and bottle count information for each array element. The program should use this data to construct a Wine object and then display the information stored in the object. For guidance, here’s a sample test program:

   // pe14-1.cpp -- using Wine class with containment
   #include <iostream>
   #include "winec.h"
   int main ( void )
   {
       using std::cin;
       using std::cout;
       using std::endl;
       
       cout << "Enter name of wine: ";
       char lab[50];
       cin.getline(lab, 50);
       
       cout << "Enter number of years: ";
       int yrs;
       cin >> yrs;
       
       Wine holding(lab, yrs); // store label, years, give arrays yrs elements
       holding.GetBottles();   // solicit input for year, bottle count
       holding.Show();         // display object contents
       
       const int YRS = 3;
       int y[YRS] = {1993, 1995, 1998};
       int b[YRS] = { 48, 60, 72};
       // create new object, initialize using data in arrays y and b
       Wine more("Gushing Grape Red",YRS, y, b);
       more.Show();
       cout << "Total bottles for " << more.Label() // use Label() method
       << ": " << more.sum() << endl;               // use sum() method
       cout << "Bye\n";
       return 0;
   }

   And here’s some sample output:

   Enter name of wine: Gully Wash
   Enter number of years: 4
   Enter Gully Wash data for 4 year(s):
   Enter year: 1988
   Enter bottles for that year: 42
   Enter year: 1994
   Enter bottles for that year: 58
   Enter year: 1998
   Enter bottles for that year: 122
   Enter year: 2001
   Enter bottles for that year: 144
   Wine: Gully Wash
   Year Bottles
   1988 42
   1994 58
   1998 122
   2001 144
   Wine: Gushing Grape Red
   Year Bottles
   1993 48
   1995 60
   1998 72
   Total bottles for Gushing Grape Red: 180
   Bye

2. This exercise is the same as Programming Exercise 1, except that you should use private inheritance instead of containment. Again, a few typedefs might prove handy. Also you might contemplate the meaning of statements such as the following:

   PairArray::operator=(PairArray(ArrayInt(),ArrayInt()));
   cout << (const string &)(*this);

   The class should work with the same test program as shown in Programming Exercise 1.

3. Define a QueueTp template. Test it by creating a queue of pointers-to-Worker (as defined in Listing 14.10) and using the queue in a program similar to that in Listing 14.12.

4. A Person class holds the first name and the last name of a person. In addition to its constructors, it has a Show() method that displays both names. A Gunslinger class derives virtually from the Person class. It has a Draw() member that returns a type double value representing a gunslinger’s draw time. The class also has an int member representing the number of notches on a gunslinger’s gun. Finally, it has a Show() function that displays all this information.

   A PokerPlayer class derives virtually from the Person class. It has a Draw() member that returns a random number in the range 1 through 52, representing a card value. (Optionally, you could define a Card class with suit and face value members and use a Card return value for Draw().) The PokerPlayer class uses the Person show() function. The BadDude class derives publicly from the Gunslinger and PokerPlayer classes. It has a Gdraw() member that returns a bad dude’s draw time and a Cdraw() member that returns the next card drawn. It has an appropriate Show() function. Define all these classes and methods, along with any other necessary methods (such as methods for setting object values) and test them in a simple program similar to that in Listing 14.12.

5. Here are some class declarations:

       // emp.h -- header file for abstr_emp class and children
       #include <iostream>
       #include <string>
       class abstr_emp
       {
       private:
           std::string fname; // abstr_emp's first name
           std::string lname; // abstr_emp's last name
           std::string job;
       public:
           abstr_emp();
           abstr_emp(const std::string & fn, const std::string & ln,
           const std::string & j);
           virtual void ShowAll() const; // labels and shows all data
           virtual void SetAll();        // prompts user for values
           friend std::ostream &
           operator<<(std::ostream & os, const abstr_emp & e);
           // just displays first and last name
           virtual ~abstr_emp() = 0; // virtual base class
       };
   
       class employee : public abstr_emp
       {
       public:
           employee();
           employee(const std::string & fn, const std::string & ln,
               const std::string & j);
           virtual void ShowAll() const;
           virtual void SetAll();
       };
   
       class manager: virtual public abstr_emp
       {
       private:
           int inchargeof; // number of abstr_emps managed
       protected:
           int InChargeOf() const { return inchargeof; } // output
           int & InChargeOf(){ return inchargeof; }      // input
       public:
           manager();
           manager(const std::string & fn, const std::string & ln,
               const std::string & j, int ico = 0);
           manager(const abstr_emp & e, int ico);
           manager(const manager & m);
           virtual void ShowAll() const;
           virtual void SetAll();
       };
   
       class fink: virtual public abstr_emp
       {
       private:
           std::string reportsto; // to whom fink reports
           protected:
           const std::string ReportsTo() const { return reportsto; }
           std::string & ReportsTo(){ return reportsto; }
       public:
           fink();
           fink(const std::string & fn, const std::string & ln,
               const std::string & j, const std::string & rpo);
           fink(const abstr_emp & e, const std::string & rpo);
           fink(const fink & e);
           virtual void ShowAll() const;
           virtual void SetAll();
       };
   
       class highfink: public manager, public fink // management fink
       {
       public:
           highfink();
           highfink(const std::string & fn, const std::string & ln,
               const std::string & j, const std::string & rpo,
               int ico);
           highfink(const abstr_emp & e, const std::string & rpo, int ico);
           highfink(const fink & f, int ico);
           highfink(const manager & m, const std::string & rpo);
           highfink(const highfink & h);
           virtual void ShowAll() const;
           virtual void SetAll();
       };

   Note that the class hierarchy uses MI with a virtual base class, so keep in mind the special rules for constructor initialization lists for that case. Also note the presence of some protected-access methods. This simplifies the code for some of the highfink methods. (Note, for example, that if highfink::ShowAll() simply calls fink::ShowAll() and manager::ShowAll(), it winds up calling abstr_emp::ShowAll() twice.) Provide the class method implementations and test the classes in a program. Here is a minimal test program:

   // pe14-5.cpp
   // useemp1.cpp -- using the abstr_emp classes
   
   #include <iostream>
   using namespace std;
   #include "emp.h"
   
   int main(void)
   {
       employee em("Trip", "Harris", "Thumper");
       cout << em << endl;
       em.ShowAll();
       
       manager ma("Amorphia", "Spindragon", "Nuancer", 5);
       cout << ma << endl;
       ma.ShowAll();
       
       fink fi("Matt", "Oggs", "Oiler", "Juno Barr");
       cout << fi << endl;
       fi.ShowAll();
       
       highfink hf(ma, "Curly Kew"); // recruitment?
       hf.ShowAll();
       
       cout << "Press a key for next phase:\n";
       cin.get();
       highfink hf2;
       hf2.SetAll();
       
       cout << "Using an abstr_emp * pointer:\n";
       abstr_emp * tri[4] = {&em, &fi, &hf, &hf2};
       for (int i = 0; i < 4; i++)
           tri[i]->ShowAll();
           
       return 0;
   }

   Why is no assignment operator defined?

   Why are ShowAll() and SetAll() virtual?

   Why is abstr_emp a virtual base class?

   Why does the highfink class have no data section?

   Why is only one version of operator<<() needed?

   What would happen if the end of the program were replaced with this code?

   abstr_emp tri[4] = {em, fi, hf, hf2};
   for (int i = 0; i < 4; i++)
       tri[i].ShowAll();