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	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
3	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; };
4	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; }; }
5	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; } }
6	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"); }
7	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? }
8	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; };
9	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!!
10	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! }
11	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; }
12	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++; }
13	Linked list example Time permitting
14	That’s a Wrap Takeaways Memberwise copy Instance allocation & deallocation Setters and getters