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/

Issues with structs

	Initialization
		Not guaranteed
		Done by hand
	Packaging datatypes & behavior
		Connecting
	Reuse / extension
		Salaried players

Basics of classes

	// An example of declaring
	// a new user defined type, using the class mech
	class MLBPlayer {
	public:
	MLBPlayer(char* name, char* team);
	private:
	enum Hit { SINGLE = 0, DOUBLE, TRIPLE, HOMER };
	char* name;
	char* team;
	int at_bats;
	int walks;
	int hits[4];
	float batting_average;
	bool bats_lefty;
	};

Basics of classes

	#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;
	strcpy(team, t);
	at_bats = walks = 0;
	bats_lefty = false;
	batting_average = 0.0;
	for (int i = 0; I < 4; i++) { hits[i] = 0; };
	}

Basics of classes

	// Moving some private fields to public for convenience
	class MLBPlayer {
	public:
	MLBPlayer(char* name, char* team);
	int at_bats;
	int walks;
	float batting_average;
	private:
	enum Hit { SINGLE = 0, DOUBLE, TRIPLE, HOMER };
	char* name;
	char* team;
	int hits[4];
	bool bats_lefty;
	};

Basics of classes

	#include <iostream>
	using namespace std;
	#include "MLBPlayer.h"
	// Accessing public member variables
	int main(int argc, char* argv[]) {
	MLBPlayer sammy_sosa("Sammy Sosa", "Chicago Cubs");
	MLBPlayer* bmd_wishes = &sammy_sosa;
	sammy_sosa.at_bats = 1;
	int total_hits = 0;
	for (int i = 0; i < 4; i++) {
	total_hits = sammy_sosa.hits[i];
	};
	bmd_wishes->batting_average =
	total_hits / bmd_wishes->at_bats;
	return 0;
	}

Basics of classes

	// Instead of public fields, let's write public accessor funcs
	class MLBPlayer {
	public:
	MLBPlayer(char* name, char* team);
	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;
	};

Basics of classes

	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;
	}
	}

Basics of classes

	float MLBPlayer::battingAverage() {
	return totalHits() / (at_bats * 1.0f);
	}
	void MLBPlayer::strikeout() {
	at_bats++;
	}

Basics of classes

	#include <iostream>
	using namespace std;
	#include "MLBPlayer.h"
	// Now using public accessor functions
	int main(int argc, char* argv[]) {
	MLBPlayer sammy_sosa("Sammy Sosa", "Chicago Cubs");
	MLBPlayer* bmd_wishes = &sammy_sosa;
	sammy_sosa.addHit(MLBPlayer::SINGLE);
	sammy_sosa.strikeout();
	sammy_sosa.strikeout();
	float ba = sammy_sosa.battingAverage();
	return 0;
	}

Basics of classes

	#include <iostream>
	using namespace std;
	#include "MLBPlayer.h"
	// Now using public accessor functions
	int main(int argc, char* argv[]) {
	MLBPlayer sammy_sosa("Sammy Sosa", "Chicago Cubs");
	MLBPlayer* bmd_wishes = &sammy_sosa;
	bmd_wishes->addHit(MLBPlayer::SINGLE);
	bmd_wishes->strikeout();
	bmd_wishes->strikeout();
	float ba = bmd_wishes->battingAverage();
	return 0;
	}

Basics of classes

	// Use overloading to define default constructor
	class MLBPlayer {
	public:
	MLBPlayer(char* name, char* team);
	MLBPlayer();
	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;
	};

Basics of classes

	#include "MLBPlayer.h"
	// Stuff elided
	MLBPlayer::MLBPlayer() {
	char* n = "Joe Schlabotnik";
	char* t = "Waffletown Syrups";
	int cnt = strlen(n) + 1;
	name = new char[cnt];
	strcpy(name, n);
	cnt = strlen(t) + 1;
	strcpy(team, t);
	at_bats = walks = 0;
	bats_lefty = false;
	batting_average = 0.0;
	for (int i = 0; i < 4; i++) { hits[i] = 0 };
	}

Basics of classes

	#include <iostream>
	using namespace std;
	#include "MLBPlayer.h"
	int main(int argc, char* argv[]) {
	// Imagine all our old stuff here.
	MLBPlayer black_sox[9];
	MLBPlayer* joe_s = new MLBPlayer;
	joe_s = new MLBPlayer();
	joe_s = new MLBPlayer("Joe Schlabotnik", "Waffletown Syrups");
	return 0;
	}

Dynamic allocation

	#include <cstring>
	// Leaves us with a dangling pointer, also wastes space
	char* dup_string(char* s) {
	const int max_buf = 1024;
	char buf[max_buf];
	strcpy(buf, s);
	return buf;
	}
	// Using dynamic allocation we're okay
	char* dup_string(char* s) {
	int cnt = strlen(s) + 1;
	char* new_string = new char[cnt];
	return new_string;
	}

That’s a Wrap

	Take away
		Classes are an improved form of structs
		Know how to declare classes, define member functions
	Dynamic allocation
		Space managed by program at run time
	Binary representations