A Static Bag Container Class

1. A container class is a data type that is capable of holding a collection of items.
   
   
2. In C++, container classes can be implemented as a class, along with member functions to add, remove, and examine items.
   
   
3. The Bag Class Abstraction.
   1. This bag will be our example of a container class. This is a class where each object can contain a collection of items (such as numbers). One of the important facets of a container class is that each object begins in a known configuration. In the case of a bag, we will count on each bag being initially empty. This is called the initial state of a bag.
      
      
   2. We will use a fixed collection of operations to manipulate bags.
      1. Insert a number in the bag.
         One of the simplest operations that we permit is the action of inserting a new number into a bag.
      2. Query a bag contents
         We will have two Query methods. Is a number in the bag? How many copies of a number is in the bag?
      3. Remove a number
         The next operation is to remove a single number from the bag.
      4. Remove all members from the bag.
         Clear the bag.
      5. Another operation allows us to find out how many numbers are in the bag, what is the size of the bag?

4. Bag Class implemetation.

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   1. The header file

      ---

      //
      #ifndef _BAG_
      #define _BAG_
      
      typedef  int bag_type;
      
      class Bag {
      
      private:
         int       count;     // members in bag
         bag_type  data[20];  // data store up to 20 members
      
      public:
                 Bag();             // Constructor
         bool    insert(bag_type);  // Put a member in the bag
         bool    remove(bag_type);  // remove a member from the bag
         int     size();            // number of members in bag
         void    clear();           // remove all members from bag
         bool    inbag(bag_type);   // is a member in the bag?
         int     howmany(bag_type); // how many member in bag.
      };
      #endif
      

      ---

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   2. The Bag implementation Code

      ---

      #include "bag.h"
      #include <iostream>
      
      Bag::Bag()    // Constructor
      {
         // set the initial state of the bag
         count=0;
      }
      
      void Bag::clear()  // Clear the bag
      {
         count=0;
      }
      
      bool Bag::insert(bag_type value) //Place a value in Bag
      {
         bool reply;
         if(count <20 ) {
            data[count]=value;
            reply=true;
            count++;
         } else {
            reply=false;
         }
         return reply;
      }
      
      bool Bag::inbag(bag_type value)  // Is a value in the bag?
      {
         bool reply=false;
         int  index;
         for(index=0;index<count&& !reply;index++)
            if(data[index] == value) reply=true;
         return reply;
      }
      
      int Bag::howmany(bag_type value) //How many of element;
      {
         int thismany=0;
         int index;
         for(index=0;index<count;index++)
            if(data[index]==value) thismany++;
         return thismany;
      }
      

      
      bool Bag::remove(bag_type value)  // Remove a value
      {
         bool reply=false;
         int  index;
         if(howmany(value) == 0) return reply;
         reply=true;
         index=0;
         while(data[index] != value) index++;
         for(;index<count;index++)
            data[index]=data[index+1];
         count--;
      }
      
      int Bag::size()    // How many elements in bag?
      {
         return count;
      }
      

      ---

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   3. Driver to test the Bag

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      #include <iostream>
      #include <cstdlib>
      #include "bag.h"
      
      using namespace std;
      
      int main(int argc, char *argv[])
      {
        Bag b;
        bag_type value;
      
        cout << "Bag" << endl;
        b.insert(4);
        do {
           value=rand()%6 +1;
        } while(b.insert(value));
        cout << b.size()<< " elements in the bag" << endl;
        cout << b.howmany(4) << " fours " << endl;
        b.remove(4);
        cout << b.size()<< " elements in the bag" << endl;
        cout << b.howmany(4) << " fours " << endl;
        cout << b.howmany(5) << " fives " << endl;
        while(b.inbag(5)) b.remove(5);
        cout << b.howmany(5) << " fives " << endl;
        
        system("Pause");
        return 0;
      }
      

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5. Test Run
   Bag
   20 elements in the bag
   3 fours
   19 elements in the bag
   2 fours
   4 fives
   0 fives
   Press any key to continue . . .