Chapter 3 ADT Unsorted List

1. Chapter 3 ADT Unsorted List

2. Lecture 7

3. List Definitions Linear relationship Each element except the first has a unique predecessor, and Each element except the last has a unique successor. Length The number of items in a list; The length can vary over time.

4. List Definitions Unsorted list A list in which data items are placed in no particular order; the only relationship between data elements is the list predecessor and successor relationships. Sorted list A list that is sorted by the value in the key; There is a semantic relationship among the keys of the items in the list. Key The attributes that are used to determine the logical order of the list.

5. Abstract Data Type (ADT) • A data type whose properties (domain and operations) are specified independently of any particular implementation.

6. Data from 3 different levels Why • Application (or user) level: modeling real-life data in a specific context. • Logical (or ADT) level: abstract view of the domain and operations. • Implementation level: specific representation of the structure to hold the data items, and the coding for operations. What How

7. ADT Operations • Constructor • Transformer • Observer • Iterator

8. Sorted and Unsorted Lists UNSORTED LIST Elements are placed into the list in no particular order. • SORTED LIST • List elements are in an order that is sorted in • some way • either numerically, • alphabetically by the elements themselves, or by a component of the element • called a KEY member

9. ADT Unsorted List Operations Transformers • MakeEmpty • PutItem • DeleteItem Observers • IsFull • GetLength • GetItem Iterators • ResetList • GetNextItem change state observe state process all

10. What is a Generic Data Type? A generic data type is a type for which the operations are defined but the types of the items being manipulated are not defined. One way to simulate such a type for our UnsortedList ADT is via a user-defined class ItemType with member function ComparedTo returning an enumerated type value LESS, GREATER, or EQUAL.

11. // SPECIFICATION FILE ( unsorted.h ) #include “ItemType.h” class UnsortedType// declares a class data type { public : // 8 public member functions void UnsortedType (); bool IsFull ( ) const; int GetLength ( ) const ; // returns length of list ItemType GetItem ( ItemType item, bool& found); void PutItem ( ItemType item ); void DeleteItem ( ItemType item ); void ResetList ( ); ItemType GetNextItem (); private : // 3 private data members int length; ItemType info[MAX_ITEMS]; int currentPos; };

12. Class Constructor A special member function of a class that is implicitly invoked when a class object is defined.

13. Class Constructor Rules • A constructor cannot return a function value, and has no return value type. • A class may have several constructors. The compiler chooses the appropriate constructor by the number and types of parameters used. • Constructor parameters are placed in a parameter list in the declaration of the class object. • The parameterless constructor is the default constructor. • If a class has at least one constructor, and an array of class objects is declared, then one of the constructors must be the default constructor, which is invoked for each element in the array.

14. Private data: length info [ 0 ] [ 1 ] [ 2 ] [MAX_ITEMS-1] currentPos Class Interface Diagram UnsortedType class UnsortedType IsFull GetLength GetItem PutItem DeleteItem ResetList GetNextItem

15. // IMPLEMENTATION FILE ARRAY-BASED LIST ( unsorted.cpp ) #include “itemtype.h” void UnsortedType::UnsortedType ( ) // Pre: None. // Post: List is empty. { length = 0; } void UnsortedType::InsertItem ( ItemType item ) // Pre: List has been initialized. List is not full. // item is not in list. // Post: item is in the list. { info[length] = item; length++; } 15

16. Before Inserting Henry into anUnsorted List The item will be placed into the length location, and length will be incremented. length 3 info [ 0 ] Maxwell [ 1 ] Bradley [ 2 ] Asad [ 3 ] . . . [MAX_ITEMS-1] 16

17. After Inserting Henry into anUnsorted List length 4 info [ 0 ] Maxwell [ 1 ] Bradley [ 2 ] Asad [ 3 ] Henry . . . [MAX_ITEMS-1]

18. intUnsortedType::GetLength( ) const // Pre: List has been inititalized. // Post: Function value == ( number of elements in // list ). { return length; } boolUnsortedType::IsFull ( ) const // Pre: List has been initialized. // Post: Function value == ( list is full ). { return ( length == MAX_ITEMS ); } 18

19. ItemType UnsortedType::GetItem ( ItemType item, bool& found ) // Pre: Key member of item is initialized. // Post: If found, item’s key matches an element’s key in the list // and a copy of that element is returned; // otherwise, input item is returned. { bool moreToSearch; int location = 0; found = false; moreToSearch = ( location < length ); while ( moreToSearch && !found ) { switch ( item.ComparedTo( info[location] ) ) { case LESS : case GREATER : location++; moreToSearch = ( location < length ); break; case EQUAL : found = true; item = info[ location ]; break; } } return item; } 19

20. Getting Ivan from an Unsorted List length 4 info [ 0 ] Maxwell [ 1 ] Bradley [ 2 ] Asad [ 3 ] Henry . . [MAX_ITEMS-1] moreToSearch: true found: false location: 0

21. Getting Ivan from an Unsorted List moreToSearch: true found: false location: 1 length 4 info [ 0 ] Maxwell [ 1 ] Bradley [ 2 ] Asad [ 3 ] Henry . . [MAX_ITEMS-1]

22. Getting Ivan from an Unsorted List length 4 info [ 0 ] Maxwell [ 1 ] Bradley [ 2 ] Asad [ 3 ] Henry . . . [MAX_ITEMS-1] moreToSearch: true found: false location: 2

23. Getting Ivan from an Unsorted List length 4 info [ 0 ] Maxwell [ 1 ] Bradley [ 2 ] Asad [ 3 ] Henry . . .[MAX_ITEMS-1] moreToSearch: true found: false location: 3

24. Getting Ivan from an Unsorted List length 4 info [ 0 ] Maxwell [ 1 ] Bradley [ 2 ] Asad [ 3 ] Henry . . . [MAX_ITEMS-1] moreToSearch: false found: false location: 4

25. void UnsortedType::DeleteItem ( ItemType item ) // Pre: item’s key has been inititalized. // An element in the list has a key that matches item’s. // Post: No element in the list has a key that matches item’s. { int location = 0 ; while (item.ComparedTo (info [location] ) != EQUAL ) location++; // move last element into position where item was located info [location] = info [length - 1 ] ; length-- ; }

26. Deleting Bradley from an Unsorted List length 4 info [ 0 ] Maxwell [ 1 ] Bradley [ 2 ] Asad [ 3 ] Henry . . . [MAX_ITEMS-1] location: 0 Key Bradley has not been matched.

27. Deleting Bradley from an Unsorted List length 4 info [ 0 ] Maxwell [ 1 ] Bradley [ 2 ] Asad [ 3 ] Henry . . . [MAX_ITEMS-1] location: 1 Key Bradley has been matched.

28. Deleting Bradley from an Unsorted List length 4 info [ 0 ] Maxwell [ 1 ] Henry [ 2 ] Asad [ 3 ] Henry . . . [MAX_ITEMS-1] location: 1 Placed copy of last list element into the position where the key Bradley was before.

29. Deleting Bradley from anUnsorted List length 3 info [ 0 ] Maxwell [ 1 ] Henry [ 2 ] Asad [ 3 ] Henry . . . [MAX_ITEMS-1] location: 1 Decremented length.

30. void UnsortedType::ResetList ( ) // Pre: List has been inititalized. // Post: Current position is prior to first element in list. { currentPos = -1; } ItemTypeUnsortedType::GetNextItem () // Pre: List has been initialized. Current position is defined. // Element at current position is not last in list. // Post: Current position is updated to next position. // item is a copy of element at current position. { currentPos++; return info [currentPos]; }

31. ItemType Class Interface Diagram class ItemType ComparedTo Private data value Print Initialize

32. Specifying class ItemType // SPECIFICATION FILE ( itemtype.h ) constintMAX_ITEM = 5 ; enumRelationType { LESS, EQUAL, GREATER }; class ItemType// declares class data type { public : // 3 public member functions RelationTypeComparedTo( ItemType ) const; void Print ( ) const; void Initialize ( int number ) ; private : // 1 private data member int value ; // could be any different // type, including a class } ;

33. // IMPLEMENTATION FILE ( itemtype.cpp ) // Implementation depends on the data type of value. #include “itemtype.h” #include <iostream> RelationType Itemtype::ComparedTo(ItemType otherItem) const { if ( value < otherItem.value ) return LESS; else if ( value > otherItem.value ) return GREATER; else return EQUAL; } void ItemType::Print ( ) const { using namespace std; cout << value << endl; } void ItemType::Initialize ( int number ) { value = number; }

34. UML diagrams

35. Lecture 8

36. C++ Data Types Address pointer reference Simple Structured Integral Floating array struct union class char short int long enum float double long double 36

37. What is a pointer variable? A pointer variable is a variable whose value is the address of a location in memory. To declare a pointer variable, you must specify the type of value that the pointer will point to. For example, int* ptr;// ptr will hold the address of an int char* q;// q will hold the address of a char

38. Using a pointer variable int x; x = 12; int* ptr; ptr = &x; NOTE: Because ptr holds the address of x, we say that ptr“points to”x 2000 12 x 3000 2000 ptr

39. Unary operator * is the deference (indirection) operator int x; x = 12; int* ptr; ptr = &x; std::cout << *ptr; NOTE: The value pointed to by ptr is denoted by *ptr 2000 12 x 3000 2000 ptr

40. Using the dereference operator int x; x = 12; int* ptr; ptr = &x; *ptr = 5; // changes the value // at adddressptr to 5 2000 12 x 3000 2000 ptr 5

41. Another Example 4000 A ch 5000 4000 q char ch; ch = ‘A’; char* q; q = &ch; *q = ‘Z’; char* p; p = q; // the right side has value 4000 // now p and q both point to ch Z 6000 4000 p

42. Pointer dereferencing and member selection

43. Dynamically Allocated Data char* ptr; ptr = new char; *ptr = ‘B’; std::cout << *ptr; 2000 ptr New is an operator

44. Dynamically Allocated Data char* ptr; ptr = new char; *ptr = ‘B’; std::cout << *ptr; NOTE: Dynamic data has no variable name 2000 ptr

45. Dynamically Allocated Data char* ptr; ptr = new char; *ptr = ‘B’; std::cout << *ptr; 2000 ptr ‘B’

46. Dynamically Allocated Data char* ptr; ptr = new char; *ptr = ‘B’; std::cout << *ptr; delete ptr; 2000 ptr NOTE: Delete deallocates the memory pointed to by ptr. ?

47. what does new do? • takes a pointer variable, • allocates memory for it to point, and • leaves the address of the assigned memory in the pointer variable. • If there is no more memory, the pointer variable is set to NULL.

48. The NULL Pointer There is a pointer constant called NULL available in cstddef. NULL is not a memory address; it means that the pointer variable points to nothing. It is an error to dereference a pointer whose value is NULL. It is the programmer’s job to check for this. while (ptr != NULL) { . . .// ok to use *ptr here }

49. int* ptr = new int; *ptr = 3; ptr = new int; // changes value of ptr *ptr = 4; What happens here? 3 ptr 3 ptr 4

50. Memory Leak A memory leak occurs when dynamic memory (that was created using operator new) has been left without a pointer to it by the programmer, and so is inaccessible. int* ptr = new int; *ptr = 8; int* ptr2 = new int; *ptr2 = -5; 8 ptr -5 ptr2 How else can an object become inaccessible?