Using enums to model cardsUsing class-based enumsClient programs and the Card classHow do objects act like built-in types?Case study: the class ClockTimeUsing the class ClockTimeDesign and Implementation IssuesRelational operatorsFree functions using class methodsClass or Data invariantsImplementing similar classesNiklaus WirthWhat’s in a file, what’s in a string?Basics of the type charChar compared to intChar values as integersFiles as lines of charactersI/O, Files, chars, and troubleUsing istringstream (istrstream) objectsOther file-reading functionsState machines for readingState diagram (decomment.cpp)State machine for /* comments */Defining statesA Computer Science Tapestry9.1Using enums to model cardsConsider the declaration below from card.h, simulate playing cardclass Card{ public: enum Suit {spades, hearts, diamonds, clubs}; Card(); // default, ace of spades Card(int rank, Suit s); bool SameSuitAs(const Card& c) const; int GetRank() const; bool IsJoker() const; private: int myRank; Suit mySuit;};A Computer Science Tapestry9.2Using class-based enumsWe can’t refer to Suit, we must use Card::SuitThe new type Suit is part of the Card classUse Card::Suit to identify the type in client codeCan assign enum to int, but need cast going the other wayint rank, suit;tvector<Card> deck;for(rank=1; rank < 52; rank++){for(suit = Card::spades;suit <= Card::clubs; suit++){ Card c(rank % 13 + 1, Card::Suit(suit)); deck.push_back(c);}}A Computer Science Tapestry9.3Client programs and the Card classDo we need to know about enums to write isFlush()?In a flush, all cards are the same suitSee card.h online, more functions than on previous slideWhat about SameSuitAs function?What about GetRank function?Think behavior before state, do we need the suit?Can cards be compared for ==? What about <?Why would we need these operators?How do we write poker hand three-of-a-kind?What about full house?A Computer Science Tapestry9.4How do objects act like built-in types?We’ve used Date and Bigint objects, and in many cases used the same operations that we use on ints and doublesWe print with operator <<We add using +, +=, and ++We compare using ==, <, >In C++ class objects can be made to act like built-in types by overloading operatorsWe can overload operator << to print to streamsWe can overload operator == to compare Date objectsWe’ll develop a methodology that allows us to easily implement overloaded operators for classes Not all classes should have overloaded operatorsIs overloading + to be the union of sets a good idea?A Computer Science Tapestry9.5Case study: the class ClockTimeRepresents hours, minutes, seconds, e.g., 1:23:47 for one hour, twenty-three minutes, 47 secondsClockTime values can be added, compared, printedclass ClockTime{ public: ClockTime(); ClockTime(int secs, int mins, int hours); int Hours() const; // returns # hours int Minutes() const; // returns # minutes int Seconds() const; // returns # seconds How are values represent internally (private), what are some options?Do client program need to know the representation?A Computer Science Tapestry9.6Using the class ClockTimeThe code below shows how the class can be used, what overloaded operators are shown?int h,m,s;ClockTime total(0,0,0);ClockTime max = total; // zerowhile (cin >> h >> m >> s){ ClockTime t(s,m,h); total += t; if (t > max) { max = t; }}cout << "total time = " << total << endl;cout << "max time = " << max << endl;A Computer Science Tapestry9.7Design and Implementation IssuesConverting to a string facilitates writing to a streamWe know how to write strings, conversion to a string solves many problemsEvery class should have a toString() method – Java doesAn object could be in a bad state, 1 hour 72 min. 87 sec., How can this happen? How do we prevent bad state?Ignore illegal valuesStop the program Convert to something appropriateFor ClockTime class we’ll normalize, convert to standard formA Computer Science Tapestry9.8Relational operatorsRelational operators are implemented as free functions, not class member functions (Tapestry approach, not universal)Needed for symmetry in some cases, see Howto E for detailsWe’ll use member function Equals to implement == Print-to-stream operator << must be a free functionWe’ll use toString to implement <<, avoid using friend functionsostream & operator << (ostream & os, const ClockTime & ct);bool operator == (const ClockTime& lhs, const ClockTime& rhs);These prototypes appear in clockt.h, no code just prototypeCode in header file causes problems with multiple definitions at link timeA Computer Science Tapestry9.9Free functions using class methodsWe can implement == using the Equals method. Note that operator == cannot access myHours, not a problem, why?bool operator == (const ClockTime& lhs, const ClockTime& rhs){ return lhs.Equals(rhs);}We can implement operator << using toString()ostream & operator << (ostream & os, const ClockTime & ct)// postcondition: inserts ct onto os, returns os{ os << ct.ToString(); return os;}Similarly, implement + using +=, what about != and < ?A Computer Science Tapestry9.10Class or Data invariantsA ClockTime object must satisfy class invariant to be validData invariant true of object as viewed by client programCannot have minutes or seconds greater than 60What methods can break the invariant, how do we fix this?A private, helper function Normalize maintains the invariantvoid ClockTime::Normalize()// post: myMinutes < 60, mySeconds < 60, represents same time{ myMinutes += mySeconds/60; mySeconds %= 60; myHours += myMinutes/60; myMinutes %= 60;}A Computer Science Tapestry9.11Implementing similar classesThe class Bigint declared in bigint.h represents integers with no bound on sizeHow might values be stored in the class?What functions will be easier to implement? Why?Implementing rational numbers like 2/4, 3/5, or –22/7Similarities to ClockTime? What private data can we use to define a rational?What will be harder to implement?What about the Date class? How are its operations facilitated by conversion to absolute number of days from 1/1/1 ?A Computer Science Tapestry9.12Niklaus WirthDesigned and implemented several