1. 1 C++ Plus Data Structures Nell Dale Chapter 4 ADTs Stack and Queue Modified from the slides by Sylvia Sorkin, Community College of Baltimore County - Essex Campus

2. 2 Stacks

3. 3 Stacks of Coins and Bills

4. 4 Stacks What is a stack? l Logical (or ADT) level: A stack is an ordered group of homogeneous items (elements), in which the removal and addition of stack items can take place only at the top of the stack. l A stack is a LIFO “last in, first out” structure.

5. 5 Stacks of Boxes and Books TOP OF THE STACK

6. Stack ADT Operations l MakeEmpty -- Sets stack to an empty state. l IsEmpty -- Determines whether the stack is currently empty. l IsFull -- Determines whether the stack is currently full. l Push (ItemType newItem) -- Adds newItem to the top of the stack. l Pop (ItemType& item) -- Removes the item at the top of the stack and returns it in item. 6

7. ADT Stack Operations Transformers n MakeEmpty n Push n Pop Observers n IsEmpty n IsFull change state observe state 7

8. //---------------------------------------------------------- // SPECIFICATION FILE (stack.h) //---------------------------------------------------------- #include "bool.h" #include "ItemType.h" // for MAX_ITEMS and // class ItemType definition class StackType { public: StackType( ); // Default constructor. // POST: Stack is created and empty. void MakeEmpty( ); // PRE: None. // POST: Stack is empty. bool IsEmpty( ) const; // PRE: Stack has been initialized. // POST: Function value = (stack is empty) 8

9. // SPECIFICATION FILE continued (Stack.h) bool IsFull( ) const; // PRE: Stack has been initialized. // POST: Function value = (stack is full) void Push( ItemType newItem ); // PRE: Stack has been initialized and is not full. // POST: newItem is at the top of the stack. void Pop( ItemType& item ); // PRE: Stack has been initialized and is not empty. // POST: Top element has been removed from stack. // item is a copy of removed element. private: int top; ItemType items[MAX_ITEMS];// array of ItemType }; 9

10. 10 Private data value Print Initialize class ItemType ItemType Class/Struct Interface Diagram

11. //------------------------------------------------------- // IMPLEMENTATION FILE (Stack.cpp) //------------------------------------------------------ // Private data members of class: //int top; //ItemType items[MAX_ITEMS]; //------------------------------------------------------- #include “bool.h” #include “ItemType.h” StackType::StackType( ) //------------------------------------------------ // Default Constructor //------------------------------------------------ { top = -1; } 11

12. // IMPLEMENTATION FILE continued (Stack.cpp) //---------------------------------------------------------- void StackType::MakeEmpty( ) //--------------------------------------------------- // PRE: None. // POST: Stack is empty. //--------------------------------------------------- { top = -1; } 12

13. // IMPLEMENTATION FILE continued (Stack.cpp) //---------------------------------------------------------- bool StackType::IsEmpty( ) const //--------------------------------------------------- // PRE: Stack has been initialized. // POST: Function value = (stack is empty) //--------------------------------------------------- { return ( top == -1 ); } bool StackType::IsFull( ) const //--------------------------------------------------- // PRE: Stack has been initialized. // POST: Function value = (stack is full) //--------------------------------------------------- { return ( top == MAX_ITEMS-1 ); } 13

14. // IMPLEMENTATION FILE continued (Stack.cpp) //------------------------------------------------------------- void StackType::Push ( ItemType newItem ) //------------------------------------------------------ // PRE: Stack has been initialized and is not full. // POST: newItem is at the top of the stack. //------------------------------------------------------ { top++; items[top] = newItem; } 14

15. // IMPLEMENTATION FILE continued (Stack.cpp) //------------------------------------------------------------- void StackType::Pop ( ItemType& item ) //------------------------------------------------------ // PRE: Stack has been initialized and is not empty. // POST: Top element has been removed from stack. // item is a copy of removed element. //------------------------------------------------------ { item = items[top]; top--; } 15

16. 16 Class Interface Diagram StackType class StackType MakeEmpty Pop Push IsFull IsEmpty Private data: top [MAX_ITEMS-1]. [ 2 ] [ 1 ] items [ 0 ]

17. 17 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code Private data: top [ MAX_ITEMS-1 ]. [ 2 ] [ 1 ] items [ 0 ] letter ‘V’

18. 18 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘V’ Private data: top -1 [ MAX_ITEMS-1 ]. [ 2 ] [ 1 ] items [ 0 ]

19. 19 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘V’ Private data: top 0 [ MAX_ITEMS-1 ]. [ 2 ] [ 1 ] items [ 0 ] ‘V’

20. 20 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘V’ Private data: top 1 [ MAX_ITEMS-1 ]. [ 2 ] [ 1 ] ‘C’ items [ 0 ] ‘V’

21. 21 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘V’ Private data: top 2 [ MAX_ITEMS-1 ]. [ 2 ] ‘S’ [ 1 ] ‘C’ items [ 0 ] ‘V’

22. 22 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘V’ Private data: top 2 [ MAX_ITEMS-1 ]. [ 2 ] ‘S’ [ 1 ] ‘C’ items [ 0 ] ‘V’

23. 23 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘S’ Private data: top 1 [ MAX_ITEMS-1 ]. [ 2 ] ‘S’ [ 1 ] ‘C’ items [ 0 ] ‘V’

24. 24 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘S’ Private data: top 2 [ MAX_ITEMS-1 ]. [ 2 ] ‘K’ [ 1 ] ‘C’ items [ 0 ] ‘V’

25. 25 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘S’ Private data: top 2 [ MAX_ITEMS-1 ]. [ 2 ] ‘K’ [ 1 ] ‘C’ items [ 0 ] ‘V’

26. 26 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘K’ Private data: top 1 [ MAX_ITEMS-1 ]. [ 2 ] ‘K’ [ 1 ] ‘C’ items [ 0 ] ‘V’

27. 27 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘K’ Private data: top 1 [ MAX_ITEMS-1 ]. [ 2 ] ‘K’ [ 1 ] ‘C’ items [ 0 ] ‘V’

28. 28 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘C’ Private data: top 0 [ MAX_ITEMS-1 ]. [ 2 ] ‘K’ [ 1 ] ‘C’ items [ 0 ] ‘V’

29. 29 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘C’ Private data: top 0 [ MAX_ITEMS-1 ]. [ 2 ] ‘K’ [ 1 ] ‘C’ items [ 0 ] ‘V’

30. 30 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); Tracing Client Code letter ‘V’ Private data: top -1 [ MAX_ITEMS-1 ]. [ 2 ] ‘K’ [ 1 ] ‘C’ items [ 0 ] ‘V’

31. 31 charletter = ‘V’; StackType charStack; charStack.Push(letter); charStack.Push(‘C’); charStack.Push(‘S’); if ( !charStack.IsEmpty( )) charStack.Pop(letter); charStack.Push(‘K’); while (!charStack.IsEmpty( )) charStack.Pop(letter); End of Trace letter ‘V’ Private data: top -1 [ MAX_ITEMS-1 ]. [ 2 ] ‘K’ [ 1 ] ‘C’ items [ 0 ] ‘V’

32. 32 What is a Class Template? l A class template allows the compiler to generate multiple versions of a class type by using type parameters. l The formal parameter appears in the class template definition, and the actual parameter appears in the client code. Both are enclosed in pointed brackets,.

33. // Laboratory 4, Class declaration... listarr.h... template class List { public: List ( int maxNumber = defMaxListSize ); ~List (); void insert ( const LE &newElement ); void remove ();... LE getCursor () const; // Return element.. void moveToNth ( int n ); // InLab 2 int find ( const LE &searchElement ); // InLab 3 private: // Data members int maxSize, size, cursor; LE *element; // Array containing the list elements }; 33

34. // Laboratory 4, Class implementation... listarr.cpp #include #include "listarr.h" //-------------------------------------------- template List :: List ( int maxNumber ) // Creates an empty list. Allocates enough memory for maxNumber // elements (defaults to defMaxListSize). : maxSize(maxNumber),size(0),cursor(-1) { element = new LE [ maxSize ]; assert ( element != 0 ); } //----------------------------------------------- template List :: ~List () // Frees the memory used by a list. { delete [] element; } //------------------------------------------------... 34

35. //Laboratory 4, Client code: test4.cpp (modified) #include #include "listarr.cpp" void main() { List testList_char(8); // Test list List testList_int(10); // Test list char testElement_char; // List element int testElement_int; // List element... } 35

36. List testList_char(8); [ 7 ]. [ 3 ] B [ 2 ] A [ 1 ] R element [ 0 ] M 36 ACTUAL PARAMETER

37. List testList_int(10); [ 9 ]. [ 3 ] 789 [ 2 ] -56 [ 1 ] 132 element [ 0 ] 5670 37 ACTUAL PARAMETER

38. Using class templates l The actual parameter to the template is a data type. Any type can be used, either built-in or user-defined. 38

39. 39 Pointer Types Recall that … char msg [ 8 ]; msg is the base address of the array. We say msg is a pointer because its value is an address. It is a pointer constant because the value of msg itself cannot be changed by assignment. It “points” to the memory location of a char. msg [0] [1] [2] [3] [4] [5] [6] [7] ‘H’ ‘e’ ‘l’ ‘l’ ‘o’ ‘\0’ 6000

40. 40 Addresses in Memory l When a variable is declared, enough memory to hold a value of that type is allocated for it at an unused memory location. This is the address of the variable. int x; float number; char ch; 2000 2002 2006 x number ch

41. 41 Obtaining Memory Addresses l The address of a non-array variable can be obtained by using the address-of operator &. int x; float number; char ch; cout << “Address of x is “ << &x << endl; cout << “Address of number is “ << &number << endl; cout << “Address of ch is “ << &ch << endl;

42. 42 What is a pointer variable? l A pointer variable is a variable whose value is the address of a location in memory. l 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

43. 43 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

44. 44 2000 12 x 3000 2000 ptr int x; x = 12; int* ptr; ptr = &x; cout << *ptr; NOTE: The value pointed to by ptr is denoted by *ptr Unary operator * is the deference (indirection) operator

45. 45 int x; x = 12; int* ptr; ptr = &x; *ptr = 5; // changes the value // at adddress ptr to 5 Using the dereference operator 2000 12 5 x 3000 2000 ptr

46. 46 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 Another Example 4000 A Z ch 5000 6000 4000 4000 q p

47. 47 C++ Data Types Structured array struct union class Address pointer reference Simple IntegralFloating char short int long enum float double long double

48. 48 The NULL Pointer There is a pointer constant 0 called the “null pointer” denoted by NULL in stddef.h But NULL is not memory address 0. NOTE: It is an error to dereference a pointer whose value is NULL. Such an error may cause your program to crash, or behave erratically. It is the programmer’s job to check for this. while (ptr != NULL) {... // ok to use *ptr here }

49. 49 Allocation of memory STATIC ALLOCATION Static allocation is the allocation of memory space at compile time. DYNAMIC ALLOCATION Dynamic allocation is the allocation of memory space at run time by using operator new.

50. 50 3 Kinds of Program Data l STATIC DATA: memory allocation exists throughout execution of program. static long SeedValue; l AUTOMATIC DATA: automatically created at function entry, resides in activation frame of the function, and is destroyed when returning from function. DYNAMIC DATA: explicitly allocated and deallocated during program execution by C++ instructions written by programmer using unary operators new and delete

51. Using operator new If memory is available in an area called the free store (or heap), operator new allocates the requested object or array, and returns a pointer to (address of ) the memory allocated. Otherwise, the null pointer 0 is returned. The dynamically allocated object exists until the delete operator destroys it. 51

52. 52 2000 ptr Dynamically Allocated Data char* ptr = 0; ptr = new char; *ptr = ‘B’; cout << *ptr;

53. 53 Dynamically Allocated Data char* ptr; ptr = new char; *ptr = ‘B’; cout << *ptr; NOTE: Dynamic data has no variable name 2000 ptr

54. 54 Dynamically Allocated Data char* ptr; ptr = new char; *ptr = ‘B’; cout << *ptr; NOTE: Dynamic data has no variable name 2000 ptr ‘B’

55. 55 Dynamically Allocated Data char* ptr; ptr = new char; *ptr = ‘B’; cout << *ptr; delete ptr; 2000 ptr NOTE: Delete deallocates the memory pointed to by ptr. ?

56. The object or array currently pointed to by the pointer is deallocated, and the pointer is considered unassigned. The memory is returned to the free store. Square brackets are used with delete to deallocate a dynamically allocated array of classes. Using operator delete 56

57. Some C++ pointer operations Precedence Higher -> Select member of class pointed to Unary: ++ -- ! * new delete Increment, Decrement, NOT, Dereference, Allocate, Deallocate + - Add Subtract >= Relational operators == != Tests for equality, inequality Lower = Assignment

58. 58 Dynamic Array Allocation char *ptr; // ptr is a pointer variable that // can hold the address of a char ptr = new char[ 5 ]; // dynamically, during run time, allocates // memory for 5 characters and places into // the contents of ptr their beginning address ptr 6000

59. 59 Dynamic Array Allocation char *ptr ; ptr = new char[ 5 ]; strcpy( ptr, “Bye” ); ptr[ 1 ] = ‘u’; // a pointer can be subscripted cout << ptr[ 2] ; ptr 6000 ‘B’ ‘y’ ‘e’ ‘\0’ ‘u’

60. 60 Dynamic Array Deallocation char *ptr ; ptr = new char[ 5 ]; strcpy( ptr, “Bye” ); ptr[ 1 ] = ‘u’; delete [ ] ptr; // deallocates array pointed to by ptr // ptr itself is not deallocated, but // the value of ptr is considered unassigned ptr ?

61. 61 int* ptr = new int; *ptr = 3; ptr = new int; // changes value of ptr *ptr = 4; What happens here? 3 ptr 3 ptr 4

62. 62 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; How else can an object become inaccessible? 8 ptr -5 ptr2

63. 63 Causing a Memory Leak int* ptr = new int; *ptr = 8; int* ptr2 = new int; *ptr2 = -5; ptr = ptr2; // here the 8 becomes inaccessible 8 ptr -5 ptr2 8 ptr -5 ptr2

64. 64 occurs when two pointers point to the same object and delete is applied to one of them. int* ptr = new int; *ptr = 8; int* ptr2 = new int; *ptr2 = -5; ptr = ptr2; A Dangling Pointer 8 ptr -5 ptr2 FOR EXAMPLE,

65. 65 int* ptr = new int; *ptr = 8; int* ptr2 = new int; *ptr2 = -5; ptr = ptr2; delete ptr2; // ptr is left dangling ptr2 = NULL; Leaving a Dangling Pointer 8 ptr -5 ptr2 8 ptr NULL ptr2

66. 66 Queues What is a queue? l Logical (or ADT) level: A queue is an ordered group of homogeneous items (elements), in which new elements are added at one end (the rear), and elements are removed from the other end (the front). l A queue is a FIFO “first in, first out” structure.

67. Queue ADT Operations l MakeEmpty -- Sets queue to an empty state. l IsEmpty -- Determines whether the queue is currently empty. l IsFull -- Determines whether the queue is currently full. l Enqueue (ItemType newItem) -- Adds newItem to the rear of the queue. l Dequeue (ItemType& item) -- Removes the item at the front of the queue and returns it in item. 67

68. ADT Queue Operations Transformers n MakeEmpty n Enqueue n Dequeue Observers n IsEmpty n IsFull change state observe state 68

69. Queue Designs 69

70. Queue Designs Queue can be stored in a l Static array – with its size fixed at compile time or l Dynamically allocated array – with its size determined at run time. 70

71. 71 DYNAMIC ARRAY IMPLEMENTATION QueType ~QueType Enqueue Dequeue. class QueType Private Data: front 1 rear 4 maxQue 5 items ‘C’ ‘X’ ‘J’ items [0] [1] [2] [3] [4] RESERVED

72. //-------------------------------------------------------- // CLASS TEMPLATE DEFINITION FOR CIRCULAR QUEUE (queue.h) #include "ItemType.h" // for ItemType template class QueType { public: QueType( ); QueType( int max );// PARAMETERIZED CONSTRUCTOR ~QueType( ) ;// DESTRUCTOR... bool IsFull( ) const; void Enqueue( ItemType item ); void Dequeue( ItemType& item ); private: int front; int rear; int maxQue; ItemType* items; // DYNAMIC ARRAY IMPLEMENTATION }; 72

73. //--------------------------------------------------- // SPECIFICATION FILE (stack.h) //--------------------------------------------------- #include "bool.h" #include "ItemType.h" // for MAX_ITEMS and // class ItemType definition class StackType { public: … private: int top; ItemType items[MAX_ITEMS];//STATIC ARRAY IMPLEMENTATION }; 73 Compare to …

74. //-------------------------------------------------------- // CLASS TEMPLATE DEFINITION FOR CIRCULAR QUEUE cont’d //-------------------------------------------------------- template QueType ::QueType( int max ) // PARAMETERIZED { maxQue = max + 1; front = maxQue - 1; rear = maxQue - 1; items = new ItemType[maxQue]; // dynamically allocates } template bool QueType ::IsEmpty( ) { return ( rear == front ) } 74

75. //-------------------------------------------------------- // CLASS TEMPLATE DEFINITION FOR CIRCULAR QUEUE cont’d //-------------------------------------------------------- template QueType ::~QueType( ) { delete [ ] items; // deallocates array }. template bool QueType ::IsFull( ) {// WRAP AROUND return ( (rear + 1) % maxQue == front ) } 75

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