CMSC 202

1. CMSC 202 Computer Science II for Majors

2. Topics • Templates • Linked Lists

3. Templates • Templates allow us to create a family of functions or classes • Templates enable programmers to create entire range of related functions or related classes • e.g. • Class template for array class would enable us to create arrays of various data types like int, float • Function template for mul() function would enable us to multiply numbers of various data types like int, float

4. Templates … cont • Templates and polymorphism • We have seen how to achieve Compile time polymorphism and Run time polymorphism • Template is a type of compile time polymorphism • Template is defined with a parameter that would be replaced by specified data type at time of actual use • Thus template is a method of achieving compile time polymorphism through parameters

5. Function Templates • Function templates are used to create a family of functions with different argument types • We want to write a function swap() in order to swap values of different data types • Function overloading void swap ( const int& m, const int& n ); void swap ( const float& m, const float& n ); void swap ( const myClass& m, const myClass& n); and invoke it as swap(num1, num2);

6. Function Templates … cont • Redundancy: we need to write implementation of swap() multiple times although the basic algorithm is same • Function templates enable us to write just one function instead of all swap() functions template <class T> ReturnType FunctionName (arguments of type T) { // Code // Use type T wherever appropriate }

7. Function Templates … cont • Function template for our swap() function template <class T> void swap ( T& x, T& y) { T temp = x; x = y; y = temp; } • Invoke function like any ordinary function swap ( a, b ); // a, b can be of any type

8. Class Templates • Class templates are used to create generic classes • They work with any data type (basic or programmer-defined) • Consider we want to build a vector class • Enable us to declare vector of integers • Has a constructor and a member function to push integer values into vector

9. Class Templates … cont class MyVector { public: vector (int size = 0) // Constructor { m_size = size; m_v = new int [m_size]; for (int i=0; i < m_size; i++) m_v[i] = 0; // initialize vector to 0 } void PushBack (int value) // push value onto vector { m_v[m_size] = value; m_size++; } private: int *m_v; int m_size; };

10. Class Templates … cont • Our MyVector class will create a vector of integers • But what if we want a vector of floats or a vector of Complex objects • Simple, replace the appropriate int by float • Still better, use Class Template – create a framework which could be used for any type

11. Class Templates … cont • General form template <class T> class ClassName { // code // Use type T wherever appropriate };

12. Class Templates … cont template <class T> class MyVector { public: vector (int size = 0) // Constructor { m_size = size; m_v = new T [m_size]; for (int i=0; i < m_size; i++) m_v[i] = 0; // initialize vector to 0 } void PushBack (T value) // push value onto vector { m_v[m_size] = value; m_size++; } private: T *m_v; int m_size; };

13. Class Templates … cont • Thus we can declare vectors of any types • Using MyVector class template MyVector <int> v1(10); // vector of int of size 10 MyVector <float> v2(20); // vector of floats MyVector <Complex> v3(2); // vector of 2 Complex // objects and push values onto vector v1.PushBack(5); v2.PushBack(3.5);

14. Linked Lists • Lists • List is an ordered collection of homogenous elements • List is dynamic, new elements can be added, existing ones can be removed at any time • List is an Abstract Data Type • E.g. List of integers { 2, 10, 34, 48, 69, 82 } • User is not concerned with how the list is implemented

15. Lists … cont • List Operations • Create a list • Insert element into list • Remove element from list • Find position of a given element in list • Assign one list to another • Delete the list • Check if list is full • Check if list is empty • Make list empty • Display contents of list

16. Lists … cont • Designing lists • Number of elements • Upper bound • Infinite • Inserting duplicate elements • Numbering of positions • Sorted lists • How would insertion, deletion be affected ?

17. Lists … cont • Implementation • Array • Elements are physically contiguous in memory • Accessing elements is faster by using sub script e.g. array[i] • Linked List • Elements are only logically contiguous, physically a node can be anywhere in memory • Typically need to traverse linked list on per node basis to access elements

18. Linked Lists • Linked list is a linear collection of nodes which are connected by pointers • Linked list is a chain of nodes • Node has at least two members • Data • Pointer to next node in list • Such lists are called Singly Linked List • Also have Doubly Linked List, Circular Linked Lists

19. Linked Lists … cont • Linked Lists in C++ • A class with public methods which define different operations to be performed on list • Pointer to first node in list is needed (Head) • Other members like tail pointer etc • Another class for representing nodes in the linked list • Pointer to next node is necessary

20. Linked Lists … cont class Node { private: Node( int d = 0, Node* n = NULL ); int m_data; Node* m_next; friend class SLList; // We want SLList to access nodes }; class SLList { public: // public methods to implement list operations private: int m_capacity; int m_size; Node *m_head;};

21. Linked Lists … cont • Representation Head Next Next Next SLList Object Node Object

22. Linked Lists … cont • Adding new node • Add at front of list • Add at end of list • Use a Tail pointer, which always points to last node in list Tail Head Next Next Next

23. Linked Lists … cont • Deleting Node • Node to be deleted is Head • Store the Head pointer in a temporary one • Advance Head (m_head = m_head -> m_next) • Delete temporary pointer • Node to be deleted is neither of above cases • Connect previous node to next node • Delete the current node

24. Linked Lists … cont • Deleting Nodes • Node to be deleted is Tail • Store Tail pointer in temporary one • Obtain the previous node of Tail ( expensive operation, need to traverse almost entire list ) • Make previous node as Tail, which points to NULL • Delete temporary pointer