1	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/
2	Issues with structs Initialization Not guaranteed Done by hand Packaging datatypes & behavior Connecting Reuse / extension Salaried players
3	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; };
4	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; }; }
5	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; };
6	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; }
7	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; };
8	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; } }
9	Basics of classes float MLBPlayer::battingAverage() { return totalHits() / (at_bats * 1.0f); } void MLBPlayer::strikeout() { at_bats++; }
10	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; }
11	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; }
12	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; };
13	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 }; }
14	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; }
15	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; }
16	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