CS 211:
Introduction to Computer Programming II

	Instructor: Brian M. Dennis
	Teaching Assistants:
	Tom Lechner, Bin Lin, Rachel Goldsborough
	http://www.cs.northwestern.edu/~bmd/cs211/

C++ Class Mechanism

	Data abstraction feature
	User defined datatype
	Collection
		Compound data
	Heterogeneous
	Typed fields
	Indexed by name
	Access control
		Information hiding
	Controlled initialization + deallocation
	Encapsulation
		data + operations on that data

Class basics

	// Use overloading to define default constructor
	class MLBPlayer {
	public: // Access specifier
	MLBPlayer(char* name, char* team); // Constructor
	MLBPlayer();  // Default constructor
	// Member functions
	int totalHits();
	float battingAverage();
	void addHit(int hit);
	void strikeout();
	enum Hit { SINGLE = 0, DOUBLE, TRIPLE, HOMER };
	private:
	// Member variables
	char* name; char* team;
	int at_bats; int walks;
	int hits[4];
	float batting_average; bool bats_lefty;
	};

Class basics

	#include "MLBPlayer.h"
	#include <cstring>
	MLBPlayer::MLBPlayer(char* n, char* t)
	{
	int cnt = strlen(n) + 1;
	name = new char[cnt];
	strcpy(name, n);
	cnt = strlen(t) + 1;
	team = new char[cnt];  // fixed up from last lecture
	strcpy(team, t);
	at_bats = walks = 0;
	bats_lefty = false;
	batting_average = 0.0;
	for (int i = 0; I < 4; i++) { hits[i] = 0; };
	}

Class basics

	int MLBPlayer::totalHits() {
	int hits_count = 0;
	for (int i = 0; i < 4; i++) {
	hits_count += hits[i];
	}
	return hits_count;
	}
	void MLBPlayer::addHit(int hit) {
	at_bats++;
	if ((SINGLE <= hit) && (hit <= HOMER)) {
	hits[hit] += 1;
	}
	}

Memberwise copy

	#include "MLBPlayer.h"
	#include <cstring>
	int main(int argc, char* argv[]) {
	MLBPlayer cubs_starters[9];
	cubs_starters[0] = MLBPlayer("Corey Patterson",
	"Chicago Cubs");
	…
	cubs_starters[3] = MLBPlayer("Sammy Sosa",
	"Chicago Cubs");
	…
	pinch_hit(8, "Tom Goodwin");
	}

Instance deallocation

	// stuff from above
	bool pinch_hit(int pos, char* name,
	MLBPlayer* lineup) {
	MLBPlayer on_deck(name,        lineup[pos].getTeam());
	if (!calledBack(name)) {
	lineup[pos] = on_deck;
	return false;
	} else {
	return true;
	}
	// What happens to on_deck here?
	}

Destructors

	class MLBPlayer {
	public:
	MLBPlayer(char* name, char* team);
	MLBPlayer();
	~MLBPlayer(); // Destructor for the class
	enum Hit { SINGLE = 0, DOUBLE, TRIPLE, HOMER }; int totalHits();
	float battingAverage();
	void addHit(int hit);
	void strikeout();
	private:
	char* name; char* team;
	int at_bats; int walks; int hits[4];
	float batting_average;
	bool bats_lefty;
	};

Destructors

	// Defining the (and only) constructor
	// for a class
	MLBPlayer::~MLBPlayer() {
	delete team; // Give back space for team
	delete name; // Give back space for name
	}
	// Except now we have another problem!!

Destructors

	// stuff from above
	bool pinch_hit(int pos, char* name,
	MLBPlayer* lineup) {
	MLBPlayer on_deck(name,   lineup[pos].getTeam());
	if (!calledBack(name)) {
	lineup[pos] = on_deck; // But we member copied!
	return false;
	} else {
	return true;
	}
	// On deck gets cleaned up!
	}

Some delete examples

	#include "MLBPlayer.h"
	#include <cstring>
	int main(int argc, char* argv[]) {
	MLBPlayer cubs_starters[9];
	MLBPlayer* leadoff_hitter = &cubs_starters[0];
	MLBPlayer* closer = new MLBPlayer("Eric Gagne",
	"LA Dodgers");
	MLBPlayers* dodgers = new MLBPlayers[9];
	delete cubs_starters;
	delete [] cubs_starters;
	delete leadoff_hitter;
	delete closer;
	delete dodgers;
	delete [] dodgers;
	}

Constructor/destructor exec

	#include "MLBPlayer.h"
	MLBPlayer ichiro("Ichiro", "Seattle Mariners");
	int main(int argc, char* argv[]) {
	MLBPlayer cubs_starters[9];
	{
	MLBPlayer local_player;
	on_injured_reserve(local_player);
	MLBPlayer* dynamic_player = new MLBPlayer;
	}
	MLBPlayer big_unit("Randy Johnson", "Diamondbacks");
	return 0;
	}
	void on_injured_reserve(MLBPlayer p) {
	static cnt = 0;
	static MLBPlayer reserve[4];
	reserve[cnt] = p;
	cnt++;
	}

Linked list example

	Time permitting

That’s a Wrap

	Takeaways
		Memberwise copy
		Instance allocation & deallocation
		Setters and getters