11-1 Computing Fundamentals with C++ Object-Oriented Programming and Design, 2nd Edition Rick Mercer Franklin, Beedle & Associates, 1999 ISBN Presentation Copyright 1999, Franklin, Beedle & Associates Students who purchase and instructors who adopt Computing Fundamentals with C++, Object-Oriented Programming and Design by Rick Mercer are welcome to use this presentation as long as this copyright notice remains intact.

11-2 Chapter 11 A Container with Iterators  Chapter Objectives  declare and use bag objects that store collections of objects  define classes with vector data members  implement member functions that manipulate vectors  implement and use iterator functions for traversing over all the items in a collection

The bag class  Programmers use many container classes  A class with the main purpose of storing a collection of elements that can be accessed  different container classes allow different access –for example a vector allows direct access to any element  Other standard containers: stack, queue, list, and map  The bag class is presented here as review of  class definitions  vectors and vector processing  It's a container class capable of storing many items

11-4 A bag class continued  A bag object as discussed in Chapter 11--there are others  stores a collection of elements that  are not in any particular order  are not necessarily unique  has operations that include bag::add bag::add bag::remove bag::remove bag::capacity bag::capacity bag::size bag::size  class definition for this bag class follows

11-5 class bag { public://--constructors bag(); bag(); bag(int capacity); bag(int capacity);//--modifiers void add(BAG_ELEMENT_TYPE newElement); void add(BAG_ELEMENT_TYPE newElement); bool remove(BAG_ELEMENT_TYPE removalCandidate); bool remove(BAG_ELEMENT_TYPE removalCandidate);//--accessors int capacity(); int capacity(); int size(); int size(); bool isEmpty(); bool isEmpty(); // -- iterator functions on next slide private: vector my_data; vector my_data; int my_size; int my_size;}; The bag class definition

11-6 The public iterator functions void first(); // post: my_index points to the first item, or if the // bag is empty, isDone would now return true void next(); // post: point to the next item, or isDone returns true bool isDone() const; // post: Returns true if collection has been traversed BAG_ELEMENT_TYPE currentItem() const; // post: Returns the item pointed to by the my_index

11-7 Client code that uses bag #include #include using namespace std; // This must precede #include "bag" (better way shown later) typedef string BAG_ELEMENT_TYPE; // <- for a bag of strings #include "bag" int main() { // This program sends all possible messages to a bag object bag bagOfStrings; bag bagOfStrings; bagOfStrings.add( "A string" ); bagOfStrings.add( "A string" ); bagOfStrings.add( "Another string" ); bagOfStrings.add( "Another string" ); bagOfStrings.add( "and still another" ); bagOfStrings.add( "and still another" ); bagOfStrings.add( "and a fourth" ); bagOfStrings.add( "and a fourth" ); bagOfStrings.remove( "and still another" ); // delete one bagOfStrings.remove( "and still another" ); // delete one bagOfStrings.remove( "I'm not in the bag!" ); // can't bagOfStrings.remove( "I'm not in the bag!" ); // can't return 0; return 0;}

11-8 A bag of ints  A bag object stores a collection objects  To store int objects for example, do this: typedef int BAG_ELEMENT_TYPE; typedef int BAG_ELEMENT_TYPE; #include "bag" #include "bag" int main() int main() { bag bagOfInts( 100 ); bag bagOfInts( 100 ); bagOfInts.add( 72 ); bagOfInts.add( 72 ); bagOfInts.add( 97 ); bagOfInts.add( 97 ); //... //...

The bag Constructors  The constructors create an empty bag bag::bag() { // Default is an empty bag with capacity 16 my_size = 0; my_size = 0; my_data.resize(16); my_data.resize(16);} bag::bag(int initialCapacity) { // Create an empty bag of any capacity desired my_size = 0; my_size = 0; my_data.resize(initialCapacity); my_data.resize(initialCapacity);} bag default; // call default constructor bag default; // call default constructor bag hold500(500); // construct with one argument bag hold500(500); // construct with one argument

The bag Modifying Member Functions  The bag::add operation adds all new elements to the "end" of the vector. If there is no room, the vector is resized void bag::add(BAG_ELEMENT_TYPE newElement) { // First, increase the bag capacity if necessary if(my_size >= my_data.capacity()) if(my_size >= my_data.capacity()) { my_capacity = 2 * my_data.capacity(); my_capacity = 2 * my_data.capacity(); my_data.resize( my_capacity ); my_data.resize( my_capacity ); } // Store argument into vector of BAG_ELEMENT_TYPEs... // Store argument into vector of BAG_ELEMENT_TYPEs... my_data[my_size] = newElement; my_data[my_size] = newElement; //...and make sure my_size is always increased by +1: //...and make sure my_size is always increased by +1: my_size++; my_size++;}

11-11 bag::remove  bag::remove uses sequential search to find the element to be removed  If the element is found  move the last element ( my_data[my_size-1] ) into the location of the removal element  decrease my_size by 1 does the following code look familiar?

11-12 bag::remove bool bag::remove(BAG_ELEMENT_TYPE removalCandidate) { int subscript = 0; int subscript = 0; // Sequentially search for removalCandidate // Sequentially search for removalCandidate while( (subscript < my_size) while( (subscript < my_size) && (my_data[subscript] != removalCandidate)) { && (my_data[subscript] != removalCandidate)) { subscript++; subscript++; } if(subscript == my_size) // removalCandidate not found if(subscript == my_size) // removalCandidate not found return false; return false; else { // move last element to removalCandidate's spot else { // move last element to removalCandidate's spot my_data[subscript] = my_data[my_size-1]; my_data[subscript] = my_data[my_size-1]; // and then decrease size by 1 // and then decrease size by 1 my_size--; my_size--; // report success to the message sender // report success to the message sender return true; return true; }}

11-13 The state of bagOfStrings before removing "Another string" Data Members State my_data[0] "A string" my_data[1] "Another string" my_data[2] "and still another" my_data[3] "and a fourth" … my_size 4 local objects in bag::remove removalCandidate "Another string" subscript 1

11-14 "Another string" The state after removing "another string" Wipe out "Another string" No longer meaningful Decrease size 1. Find removalCandidate in my_data[1] 2. Overwrite it with the "last" bag element and decrease size my_data[0] "A string" my_data[1] "And a fourth" my_data[2] "and still another" my_data[3] "And a fourth"... my_size 3

The bag Accessor functions int bag::capacity() const { // Return how many elements could be stored return my_data.capacity(); return my_data.capacity();} int bag::size() const { // Return how many elements are in the bag return my_size; return my_size;} bool bag::isEmpty() const { // Return true if there are 0 elements in the bag return my_size == 0; return my_size == 0;}

The Iterator Pattern  vectors have subscripts for iterating over all the meaningful elements  standard containers, including vectors use a separate iterator class more later  bags use member functions firstisDonecurrentItemnext

11-17 Iterating over items in a bag bag aBag; int sum = 0; int sum = 0; int n = 9; int n = 9; for(int j = 1; j <= n; j=j+2) for(int j = 1; j <= n; j=j+2) { aBag.add(j); aBag.add(j); } cout << "Iterate over the entire collection" << endl; cout << "Iterate over the entire collection" << endl; for( aBag.first(); ! aBag.isDone(); aBag.next() ) for( aBag.first(); ! aBag.isDone(); aBag.next() ) { cout.width(4); cout.width(4); // reference "current" bag element // reference "current" bag element cout << aBag.currentItem(); cout << aBag.currentItem(); // reference it again // reference it again sum = sum + aBag.currentItem(); sum = sum + aBag.currentItem(); } cout << "\nSum: " << sum << endl; cout << "\nSum: " << sum << endl; Output ? Demonstrate testbag.cpp

11-18 The iterator implementations void bag::first() { // Set internal index to reference the 1st element my_index = 0; my_index = 0;} bool bag::isDone() const { // Return true if previous next was the last element return my_index >= my_size; return my_index >= my_size;} void bag::next() { // Set internal index to reference the next element // or to allow isDone to return true // or to allow isDone to return true my_index++; my_index++;} BAG_ELEMENT_TYPE bag::currentItem() const { // Set internal index to reference the 1st element return my_data[my_index]; return my_data[my_index];}

11-19 The Iterator pattern will be repeated as are all patterns  The iterator pattern will be used again  In Chapter 13: Object-Oriented Software Development  to display all CDs in a CD collection  to display all track in a CD  In Section 14.2  iterator objects are used to traverse the elements in the standard C++ containers such as vector and list –the iterator pattern is implemented quite differently