chapter12

Chapter 12 "Classes and Dynamic Memory Allocation"

Programming Exercises

1. Consider the following class declaration:

   class Cow {
       char name[20];
       char * hobby;
       double weight;
   public:
       Cow();
       Cow(const char * nm, const char * ho, double wt);
       Cow(const Cow c&);
       ~Cow();
       Cow & operator=(const Cow & c);
       void ShowCow() const; // display all cow data
   };

   Provide the implementation for this class and write a short program that uses all the member functions.

2. Enhance the String class declaration (that is, upgrade string1.h to string2.h) by doing the following:

   a. Overload the + operator to allow you to join two strings into one.

   b. Provide a stringlow() member function that converts all alphabetic characters in a string to lowercase. (Don’t forget the cctype family of character functions.)

   c. Provide a stringup() member function that converts all alphabetic characters in a string to uppercase.

   d. Provide a member function that takes a char argument and returns the number of times the character appears in the string.

   Test your work in the following program:

   // pe12_2.cpp
   #include <iostream>
   using namespace std;
   #include "string2.h"
   int main()
   {
       String s1(" and I am a C++ student.");
       String s2 = "Please enter your name: ";
       String s3;
       cout << s2;               // overloaded << operator
       cin >> s3;                // overloaded >> operator
       s2 = "My name is " + s3;  // overloaded =, + operators
       cout << s2 << ".\n";
       s2 = s2 + s1;
       s2.stringup();            // converts string to uppercase
       cout << "The string\n" << s2 << "\ncontains " << s2.has('A')
            << " 'A' characters in it.\n";
       s1 = "red";       // String(const char *),
                         // then String & operator=(const String&)
       String rgb[3] = { String(s1), String("green"), String("blue")};
       cout << "Enter the name of a primary color for mixing light: ";
       String ans;
       bool success = false;
       while (cin >> ans)
       {
         ans.stringlow();       // converts string to lowercase
         for (int i = 0; i < 3; i++)
         {
             if (ans == rgb[i]) // overloaded == operator
             {
                 cout << "That's right!\n";
                 success = true;
                 break;
             }
         }
         if (success)
             break;
         else
             cout << "Try again!\n";
         }
         cout << "Bye\n";
         return 0;
     }

   Your output should look like this sample run:

   Please enter your name: Fretta Farbo
   My name is Fretta Farbo.
   The string
   MY NAME IS FRETTA FARBO AND I AM A C++ STUDENT.
   contains 6 'A' characters in it.
   Enter the name of a primary color for mixing light: yellow
   Try again!
   BLUE
   That's right!
   Bye

3. Rewrite the Stock class, as described in Listings 10.7 and 10.8 in Chapter 10 so that it uses dynamically allocated memory directly instead of using string class objects to hold the stock names. Also replace the show() member function with an overloaded operator<<() definition.Test the new definition program in Listing 10.9.

4. Consider the following variation of the Stack class defined in Listing 10.10:

   // stack.h -- class declaration for the stack ADT
   typedef unsigned long Item;
   
   class Stack
   {
   private:
       enum {MAX = 10};    // constant specific to class
       Item * pitems;      // holds stack items
       int size;           // number of elements in stack
       int top;            // index for top stack item
   public:
       Stack(int n = MAX); // creates stack with n elements
       Stack(const Stack & st);
       ~Stack();
       bool isempty() const;
       bool isfull() const;
       // push() returns false if stack already is full, true otherwise
       bool push(const Item & item);   // add item to stack
       // pop() returns false if stack already is empty, true otherwise
       bool pop(Item & item);          // pop top into item
       Stack & operator=(const Stack & st);
   };

   As the private members suggest, this class uses a dynamically allocated array to hold the stack items. Rewrite the methods to fit this new representation and write a program that demonstrates all the methods, including the copy constructor and assignment operator.

5. The Bank of Heather has performed a study showing that ATM customers won’t wait more than one minute in line. Using the simulation from Listing 12.10, find a value for number of customers per hour that leads to an average wait time of one minute. (Use at least a 100-hour trial period.)

6. The Bank of Heather would like to know what would happen if it added a second ATM. Modify the simulation in this chapter so that it has two queues. Assume that a customer will join the first queue if it has fewer people in it than the second queue and that the customer will join the second queue otherwise. Again, find a value for number of customers per hour that leads to an average wait time of one minute. (Note: This is a nonlinear problem in that doubling the number of ATMs doesn’t double the number of customers who can be handled per hour with a oneminute wait maximum.)