1. 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 
CS 106X – Programming Abstractions in C++
Dr. Cynthia Bailey Lee

2. 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!

3. Queue Applications
Mouse events

4. 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

5. Broad categories of ADTs

6. 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

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

8. Map

9. 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!

10. 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;

11. 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);

12. 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) (B) (C) other # (D) Error

13. 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) (B) (C) other # (D) Error

14. 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) (B) (C) other # (D) Error

15. Map Applications
Anagram finder

16. “Abstractions” Bacon artists Cab stain rots Crab in toasts
Bonsai tracts …