CS 106X – Programming Abstractions in C++                CS2 in C++ Peer Instruction Materials by Cynthia Bailey Lee is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Permissions beyond the scope of this license may be available at http://peerinstruction4cs.org. CS 106X – Programming Abstractions in C++ Dr. Cynthia Bailey Lee

Today’s Topics Quick follow-up on queues Broad categories of ADTs Map Queue Applications: Mouse event queue Broad categories of ADTs Map Returning a reference Map Applications: Anagram finder Bacon Artists!

Queue Applications Mouse events

Event queues While your code executes, a separate program is constantly listening for events and recording them Mouse moved, mouse clicked, mouse dragged, keyboard key pressed, etc Every once in a while, your code can call getNextEvent() to see what has happened getNextEvent returns the events one at a time in the same order they happened In other words, returns them in FIFO order! When it is “recording” events, it is enqueuing events in an event QUEUE Very common use of the Queue ADT

Broad categories of ADTs

Linear containers, AKA Sequential containers Array Vector Stack Queue The question “Which is the [1st/2nd/3rd…] element?” is coherent Note: even though we can’t directly access 3rd element with Stack/Queue, there is one—there is an ordering

Associative containers Map Set Lexicon The question “Which is the [1st/2nd/3rd…] element?” is not coherent They associate keys with values

Map

Redacted…until the second half of the quarter! map.h template <typename KeyType, typename ValueType> class Map { public: Map(); virtual ~Map(); int size() const; bool isEmpty() const; void put(const KeyType & key, const ValueType & value); ValueType get(const KeyType & key) const; bool containsKey(const KeyType & key) const; void remove(const KeyType & key); void clear(); ValueType & operator[](const KeyType & key); ValueType operator[](const KeyType & key) const; private: }; Redacted…until the second half of the quarter!

Review: reference parameters static void clearBoard(Grid<int> board){ for (int i=0; i<board.numRows(); i++) for (int j=0; j<board.numCols(); j++) board[i][j] = 0; } static void clearBoard(Grid<int>& board){ Grid<int> tictactoe(3,3); tictactoe[0][0] = 2; clearboard(tictactoe); cout << tictactoe[0][0] << endl;

Returning a reference C++ also allows you to define a return type to be a reference Gives you a reference to the item being returned In the case of map, this returns a reference to the value at map[key]: ValueType & operator[](const KeyType & key);

Returning a reference Predict the outcome: Map<string,Vector<int>> mymap; Vector<int> numbers; numbers.add(1); numbers.add(2); numbers.add(3); mymap["123"] = numbers; mymap["123"].add(4); cout << “New size: " << mymap["123"].size() << endl; Predict the outcome: (A) 3 (B) 4 (C) other # (D) Error

Returning a reference Predict the outcome: Map<string,Vector<int>> mymap; Vector<int> numbers; numbers.add(1); numbers.add(2); numbers.add(3); mymap["123"] = numbers; Vector<int> plainTest = mymap["123"]; plainTest.add(4); cout << “New size: " << mymap["123"].size() << endl; Predict the outcome: (A) 3 (B) 4 (C) other # (D) Error

Returning a reference Predict the outcome: Map<string,Vector<int>> mymap; Vector<int> numbers; numbers.add(1); numbers.add(2); numbers.add(3); mymap["123"] = numbers; Vector<int> referenceTest = mymap["123"]; referenceTest.add(4); cout << “New size: " << mymap["123"].size() << endl; Predict the outcome: (A) 3 (B) 4 (C) other # (D) Error

Map Applications Anagram finder

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