Designing and Using ClassesImplementing ClassesPlaying Hangman, toward a prototypeNouns, scenarios, verbsImplementing WordSourcewordsource.h, wordsource.cppGuessing lettersletters.hTesting and implementing letters.cpphang.cpp, the main/testing programProgramming Tips, Heuristics, HelpCommon interfaces are a good thingReuse concepts as well as codeRandom walksWalking behavior (see frogwalk2.cpp)Two-dimensional walkerA Computer Science Tapestry7.1Designing and Using ClassesClass implementation, summary of what we’ve seenData is private and is accessible in each member functionEach object has it’s own data, so that each of five Dice objects has its own mySides and myRollCountMember function implementations are in a .cpp file, interface is in a .h fileCompiling and linking, interface and implementationClient programs #include a .h file, this is the interfaceClient programs link the implementation, which is a compiled version of the .cpp file (.o or .obj suffix), implementations are often combined in a library, e.g., libtapestry, and the library is linkedA Computer Science Tapestry7.2Implementing ClassesDetermining what classes are needed, and how they should be implemented is difficult; designing functions is difficultExperience is a good teacher, failure is a good teacherGood design comes from experience, experience comes from bad designDesign and implementation combine into a cyclical process: design, implement, re-visit design, implement, test, redesign, …•Grow a working program, don’t do it all at the same timeOne design methodology says “look for nouns, those are classes”, and “look for verbs or scenarios, those are member functions”Not every noun is a class, not every verb is a methodA Computer Science Tapestry7.3Playing Hangman, toward a prototypeHangman is a word game, a player tries to guess a secret word one letter at a time, each missed letter counts against the player, after 8 or 10 or 12 misses the player is “hung”. Usually each miss results in drawing a body part on a gallows.Diagram shows four missesPart of 10-letter word is guessedWhat are nouns?What are verbs?What are scenarios? a m o s n t_ _ t _ _ a t _ _ _A Computer Science Tapestry7.4Nouns, scenarios, verbsGet a word to guessFrom another player, a dictionary, the webFrom a WordSourceShow the word to the player, let the player guess lettersThe word is displayed, then letters are revealed as guesses are madeClass Word, methods Display, Reveal, Guess, …Guess is also a noun, a letter is guessed, missed letters count against, good letters reveal, duplicate guesses don’t countGuessedLetters? Letters? Alphabet? Which is the noun?A Computer Science Tapestry7.5Implementing WordSourceWhat’s the simplest way to get a word from a WordSource so that we can test the rest of the programCan we design a class that’s simple to test with at first, but easy to make more realistic later (essence of prototyping)How can we guess pick one of several words at random once we’re ready to move towards a more realistic implementation?•Alternatives using small number of strings and a Dice?•Alternatives using a file of words?What should we do to test the WordSource class?Can we test without implementing the whole program?Test each class separately when possible, isolate mistakesA Computer Science Tapestry7.6wordsource.h, wordsource.cppWordSource will return a word, later add “from a file”#include <string>class WordSource{ public: WordSource(); string GetWord();}; // here’s the .cpp file#include "wordsource.h"WordSource::WordSource(){}string WordSource::GetWord(){ return "literature";}A Computer Science Tapestry7.7Guessing lettersPlayer guesses a letter, it’s in the word, or a miss, or has been guessed alreadyCreate a class Letters, have it report whether a letter has been guessed already, or a letter is in the word, or a missShould Letters report a miss/correct? If so, does Letters need to know the word? What are alternatives?Don’t worry about implementation, worry about behavior, or the interfaceEventually you’ll need to worry about implementing, what will be hardest/harder, how can we test without implementing hard part first?A Computer Science Tapestry7.8letters.hWe’ll construct an instance of Letters from a secret word/stringAsk Letters to display the “to be guessed word”Guess a letter, have Letters report if it’s in the wordOptionally report duplicate guesses, add this laterclass Letters{ public: Letters(const string& s); bool GuessLetter(const string& letter); void Display(); private: string myDisplay; // show this string string myString; // the secret word};A Computer Science Tapestry7.9Testing and implementing letters.cppGuessLetter uses string::find to determine miss/correctMust also “save state” so that Display shows guesses (and later so that duplicate guess detection works)Initially we can just return true/false to test, no state savedWe’ll test this version, but be thinking about what Letter s::GuessLette r must doChange state so that display shows guessed lettersUltimately, remember guesses to not penalize twiceWhat about determining when game is over?What about determining # misses so far? Who tracks?A Computer Science Tapestry7.10hang.cpp, the main/testing program#include <string>#include "prompt.h"#include "letters.h"#include "wordsource.h"int main(){ WordSource ws; string s = ws.GetWord(); Letters letters(s); while (true) { letters.Display(); s = PromptString("guess a letter"); if (letters.GuessLetter(s)) { cout << "that's in the word!!" << endl; } else { cout << "that's a miss" << endl; } }}A Computer Science Tapestry7.11Programming Tips, Heuristics, HelpDevelop a core working program, add to it slowlyIterative enhancement, test as you go, debug as you goDo the hard part first, or do the easy part firstWhich is best? It depends.Concentrate on behavior first when designing classes, then on stateState is useful for communicating between method callsIf you’re using several classes, you’ll need to modify the Makefile or your project in an IDE: Codewarrior/Visual C++A Computer Science Tapestry7.12Common interfaces are a good thingThe class WordStreamIterator iterates over a file returning one word/string at a