DATA STRUCTURES LAB 5 TA Nouf AlHarbi nouf

DATA STRUCTURES LAB 5 TA: Nouf Al-Harbi nouf 200@hotmail. com

DATA STRUCTURES LAB 5 Queue

objectives 3 By the end of this lab you will be able to : � Use pointers and dynamic memory allocation � Implement a queue class with all its operations Queue

4 Part 1 : Pointers & Dynamic Memory Allocation Queue

Addresses in Memory 5 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 x 2002 number 2006 ch

Obtaining Memory Addresses 6 The address of a non-array variable can be obtained by using the address-of operator &. int float char x; number; ch; cout << “Address of x is “ << &x << endl; cout << “Address of number is “ << &number << endl; cout << “Address of ch is “ << &ch << endl;

What is a pointer variable? 7 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

Using a pointer variable 8 2000 int x; x = 12; 12 x int* ptr; ptr = &x; 3000 2000 ptr NOTE: Because ptr holds the address of x, we say that ptr “points to” x

9 dereference (indirection) operator * 2000 int x; x = 12; 12 x int* ptr; ptr = &x; 3000 cout ptr << 2000 *ptr; NOTE: The value pointed to by ptr is denoted by *ptr

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

The NULL Pointer 11 Sometimes we want a pointer to point to nothing That’s called the null pointer NOTE: � � � It is an error to dereference a pointer whose value is NULL. Such an error may cause your program to crash It is the programmer’s job to check for this. while (ptr != NULL) {. . . // ok to use *ptr here }

Allocation of memory 12 STATIC ALLOCATION is the allocation of memory space at compile time. DYNAMIC ALLOCATION is the allocation of memory space at run time by using operator new.

Dynamic Memory Allocation 13 To achieve dynamic allocation of a variable, we use the C++ operator new, followed by the name of a data type: 3000 int* int. Pointer= new int; 10 *int. Pointer=10; 3000 Queue

Dynamic Array Allocation 14 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 6000 ptr

Dynamic Array Allocation 15 char *ptr ; ptr = new char[ 5 ]; strcpy( ptr, “Bye” ); ptr[ 1 ] = ‘u’; // a pointer can be subscripted cout << ptr[ 2] ; 6000 ptr ‘B’ ‘u’ ‘y’ ‘e’ ‘’

Dynamic Array Deallocation 16 char *ptr ; ptr = new char[ 5 ]; strcpy( ptr, “Bye” ); ptr[ 1 ] = ‘u’; delete ptr; ? ptr // deallocates array pointed to by ptr // ptr itself is not deallocated, but // the value of ptr is considered unassigned

17 Part 2 : Queue

Queue 18 It is an ordered group of homogeneous items of elements. Queues have two ends: � Elements are added at one end. � Elements are removed from the other end. The element added first is also removed first (FIFO: First In, First Out). Queue

Queue Operations. . 19 Make. Empty � Is. Empty � Determines whether the queue is currently full. Enqueue (Item. Type new. Item) � Determines whether the queue is currently empty. Is. Full � Sets queue to an empty state. Adds new. Item to the rear of the queue. Dequeue (Item. Type& item) � Removes the item at the front of the queue and returns it in item. Queue

20 Queue Example. . Implement a Queue of userdefined integer elements Queue

21 Que. Type class (data & methods members) 4 data members � front � � rear index immediately past the rear element Max. Que � index of the front element Number of elements in queue Private data: front max. Que Items rear [Max. Que] Items [0] [1] [2] Dynamic integer array implementation Queue

22 Que. Type class (data & methods members) Que. Type ~Que. Type Private data: Make. Empty front Enqueue Dequeue rear Is. Empty max. Que Items [0] [1] [2] [Max. Que] Is. Full Length. Is Display. Queue

Queue Example 23 0 Queue () x x. enqueue (8) x. enqueue (2) x. dequeue (y) x. enqueue (9) 2 3 4 Queue f r 0 x. enqueue (5) 1 Queue 1 2 3 4 f 0 2 4 8 1 f 4 f=1 r=3 r 3 2 f=0 r=3 2 2 8 4 r 3 2 f 1 Queue 3 2 8 f=0 r=2 r 2 1 Queue 0 3 8 5 f=0 r=1 r 1 5 f 0 Queue r=0 5 f 0 f=0 4 9 r f=1 r=4

Queue Example 24 0 x. dequeue (y) Queue 9 3 f 2 10 4 3 10 1 4 9 r 1 2 f 3 r f 1 4 9 4 r=4 1 9 2 r 1 f=2 r 4 3 f 2 10 0 x. enqueue (4) 1 4 9 2 0 x. dequeue (y) 1 f 2 Queue 3 2 r 0 x. enqueue (10) 2 Queue 0 x. enqueue (1) 1 1 f=2 r=0 f=2 r=1 f=3 r=2

Implementing Que. Type Class 25 � the class declaration is placed in one file (header file) Que. Type. h � the implementation of all the methods is put in another file Que. Type. cpp � the Main function is put in another file Queue. cpp Foe each Que. Type. cpp & Queue. cpp we should inclusde Que. Type. h file � #include “Que. Type. h” Queue