1 / 43

Chapter 3

Chapter 3. Pointers and Array-Based Lists Dr. Youssef Harrath yharrath@uob.edu.bh. Outline. Pointer Data Types and Pointer Variables Declaring Pointer Variables Address of Operator (&) Dereferencing Operator (*) Classes, structs, and Variables Initializing Pointer Variables

niran
Download Presentation

Chapter 3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 3 Pointers and Array-Based Lists Dr. YoussefHarrath yharrath@uob.edu.bh

  2. Outline • Pointer Data Types and Pointer Variables • Declaring Pointer Variables • Address of Operator (&) • Dereferencing Operator (*) • Classes, structs, and Variables • Initializing Pointer Variables • Dynamic Variables • Operations on Pointer Variables • Dynamic Arrays • Function and Pointers • Classes and Pointers: Some Pecularities • Array-Based Lists Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  3. Declaring Pointer Variables • A pointer variable is a variable whose content is an address (memory location). • Syntax: dataType *identifier; • Example1: int *p; // the content of p pointers to a memory location of the type int • Example2: int* p, q; // only p is a pointer variable • Example 3: int *p, *q; // both p and q are pointer variables Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  4. Address of Operator (&) • In C++, the symbol & is a unary operator that returns the address of its operand. int x = 25; int *p; p = &x; // assigns the address of x to p, that is x and the value of p // refer to the same memory location cout<<*p<<endl; // prints the value pointed by p which is 25 *p = 55; // changes the content of the memory location pointed by // p, that is x = 55 Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  5. Dereferencing Operator (*) Main Memory Main Memory Main Memory Main Memory int *p; int num; num = 78; p = &num; *p = 24; Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  6. Dereferencing Operator (*) Main Memory Main Memory int *p; int x; x = 50; Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  7. Dereferencing Operator (*) Main Memory Main Memory int *p; int x; x = 50; p = &x; Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  8. Dereferencing Operator (*) Main Memory Main Memory int *p; int x; x = 50; p = &x; *p = 38; Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  9. Classes, structs, and Variables • We can declare and manipulate pointers to other data types, such as classes. • Both classes and structs have the same capabilities; the only difference is that, by default, all members of a class are private and all members of a struct are public. • Therefore, the pointers can be discussed similarly for classes and structs. Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  10. Classes, structs, and Variables struct studentType { char name[27]; double gpa; int sID; char grade; }; studentType student; //student is an object of type studentType studentType* studentPtr; // studentPtr is a pointer variable of the type studentType studentPtr = &student; // stores the address of student in studentPtr (*studentPtr).gpa = 3.9; // stores 3.9 in the component gpa of the object student // equivalent to studentPtr ->gpa = 3.9; Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  11. Classes, structs, and Variables class classExample { public: void setX(int a); void print(); private: int x; }; void classExample::setX(int a) { x = a; } void classExample::print() { cout<<“x = “<<x<<endl; } int main() { classExample *cExpPtr; classExample cExpObject; cExpPtr = &cExpObject; cExpPtr ->setX(5); cExpPtr->print(); return 0; } Output: x = 5 Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  12. Initializing Pointer Variables • C++ doesn’t automatically initialize variables. • Pointers must be initialized to avoid them pointing anything. • p = 0 ; or p = NULL; are equivalent and initialize p to nothing. Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  13. Dynamic variables • Variables that are created during program execution are called dynamic variables. • With the help of pointers, C++ creates dynamic variables. • C++ provides two operators new and delete to create and destroy, respectively, dynamic variables. Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  14. Dynamic variables new dataType; // to allocate a single variable new dataType[intExp]; // to allocate an array of variables new allocates memory of the desired type and returns a pointer (the address) to it. int *p; char *q; int x; p = &x; // store the address of x in p but no new memory is allocated. p = new int; // allocate memory space of the type int and store the // address of the allocated memory in p. q = new char[16]; // create an array of 16 char and stores the base address of the array in q. Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  15. Dynamic variables char *name; // name is a pointer of the type char name = new char[5]; // allocate memory for an array of 5 char // elements and stores the base address of the array in name strcpy(name, “John”); // stores John in name delete [] name; // destroy the space memory allocated for the array name. Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  16. Operations on Pointer Variables int *p, *q; char *ch; double *d; p = q; // p and q points to the same memory location. Any changes // made to *p automatically change the value of *q and vice versa if(p ==q) // evaluates to true if p and q point to the same memory location. if(p!=q) // evaluates to true if p and q point to different memory locations. p++; // increments the value of p by 4 bytes d++; // increments the value of p by 8 bytes ch++; // increments the value of p by 1 byte Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  17. Dynamic Arrays • Static arrays have fixed size. • One of the limitations of a static array is that every time you execute the program, the size of the array is fixed (we have to change the size whenever we need) • Dynamic arrays are created during the execution. Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  18. Dynamic Arrays int *p; p = new int[10]; *p = 25; p++; *p = 35; Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  19. Functions and Pointers • A pointer variable can be passed as a parameter to a function either by value or by reference. void example(int* &p, double *q) { // both p and q are pointers. The parameter p is a // reference parameter; the parameter q is a value // parameter … } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  20. Functions and Pointers • In C++ a function can return a value of the type pointer. int* testExp(…) { // the returned type of the function is a pointer of the // type int … } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  21. Classes and Pointers: Some Pecularities class pointerDataClass { public: … private: int x; intlenP; int *p; }; pointerDataClassobjectOne; pointerDataClassobjectTwo; Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  22. Classes and Pointers: Some Pecularities objectOne objectTwo x x lenP lenP p p … p = newint[10]; // dynamic array … 5 36 24 15 … Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  23. Classes and Pointers: Some Pecularities class pointerDataClass { public: ~pointerDataClass(); // destructor to deallocate the dynamic array // pointed by p … private: int x; intlenP; int *p; }; pointerDataClass:: ~pointerDataClass() { delete [] p; } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  24. Classes and Pointers: Some Pecularities Problem If objectTwo.p deallocates the memory to which it points, objectOne.p would become invalid Solution Overload the assignment operator … p = newint[10]; // dynamic array … objectTwo = objectOne; objectOne objectTwo x x lenP lenP p p 5 36 24 15 … Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  25. Classes and Pointers: Some Pecularities objectOne objectTwo x x lenP lenP p p 5 5 36 36 24 24 15 15 … … Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  26. Classes and Pointers: Some Pecularities • General Syntax to overload the Assignment Operator (=) for a Class: const className& operator=()const className&; const className&::operator=(const className& rightObject) { // local declaration, if any if(this != &rightObject) // avoid self-assignement { // algorithm to copy rightObject into this object } return *this; // return the object assigned } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  27. Classes and Pointers: Some Pecularities Example Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  28. Array-Based Lists • A list is a collection of elements of the same type. • The length of a list is the number of elements in the list. • Following are some operations performed on a list: • Create the list. The list is initialized to any empty state. • Determine whether the list is empty. • Determine whether the list is full. • Find the size of the list. • Destroy, or clear, the list. • Insert an item at a given position. • Search the list for a given item. • … Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  29. Array-Based Lists • Because all the elements of a list are of the same type, they will be stored in an array. • To process a list in an array, we need the following three variables: • The array holding the list elements. • A variable to store the length of the list (that is, the number of list elements currently in the array). • A variable to store the size of the array (that is, the maximum number of elements that can be stored in the array). Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  30. Array-Based Lists: UML diagram arrayListType #*list: elemType #length: int #maxSize: int +isEmty(): bool +isFull(): bool +listSize(): int +maxListSize(): int +print() const: void +isItemAtEqual(int, const elemType&): bool +insertAt(int, const elemType&): void +insertEnd(const elemType&): void +removeAt(int): void +retrieveAt(int, elemType&): void +replaceAt(int, const elemType&): void +clearList(): void +seqSearch(const elemType&): int +insert(const elemType&): void +remove(const elemType&): void +arrayListType(int = 100) +arrayListType(const arrayListType<elemType>&) +~arrayListType() +operator=(const arrayListType<elemType>&): const arrayListType<elemType>& Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  31. Array-Based Lists: isEmpyt() and isFull() template<class elemType> boolarrayListType<elemType>::isEmpty() { return (length == 0); } template<class elemType> boolarrayListType<elemType>::isFull() { return (length == maxSize); } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  32. Array-Based Lists: listSize() and maxListSize() template<class elemType> intarrayListType<elemType>::listSize() { return length ; } template<class elemType> intarrayListType<elemType>::maxListSize() { return maxSize; } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  33. Array-Based Lists: print() and isItemAtEqual() template<class elemType> void arrayListType<elemType>::print() const { for(inti = 0; i < length; i++) cout<<list[i]<<“ “; cout<<endl; } template<class elemType> boolarrayListType<elemType>::isItemAtEqual(int location, const elemType& item) { return(list[location] == item); } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  34. Array-Based Lists: insertAt() template<class elemType> void arrayListType<elemType>::insertAt(int location, const elemType& insertItem) { if(location < 0 || location >= maxSize) cerr<<“The position of the item to be inserted is out of range.”<<endl; else if(length >= maxSize) // the list is full cout<<“Cannot insert in a full list.<<endl; else { for(inti = length; i > location; i--) list[i] = list[i-1]; // shift the elements each one position to the right list[location] = insertItem; // insert the item at the specified position length++; } } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  35. Array-Based Lists: insertEnd() template<class elemType> void arrayListType<elemType>::insertEnd(const elemType& insertItem) { if(length >= maxSize) // the list if full cout<<“Cannot insert in a full list.<<endl; else { list[length] = insertItem; // insert the item at the end length++; } } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  36. Array-Based Lists: removeAt() template<class elemType> void arrayListType<elemType>::removeAt(int location) { if(location < 0 || location >= length) cout<<“The location of the item to be removed is out of range.”<<endl; else { for(inti = location; i < length - 1; i++) list[i] = list[i+1]; length--; } } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  37. Array-Based Lists: retrieveAt() and replaceAt() template<class elemType> void arrayListType<elemType>::retrieveAt(int location, elemType& retItem) { if(location < 0 || location >= length) cout<<“The location of the item to be retrieved is out of range.”<<endl; else { retItem = list[location]; } } template<class elemType> void arrayListType<elemType>::replaceAt(int location, const elemType& repItem) { if(location < 0 || location >= length) cout<<“The location of the item to be retrieved is out of range.”<<endl; else { list[location] = repItem; } } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  38. Array-Based Lists: clearList() and arrayListType() template<class elemType> void arrayListType<elemType>::clearList() { length = 0; } template<class elemType> arrayListType<elemType>::arrayListType(int size) { if(size < 0) { cout<<“The array size must be positive. Creating of an array of size 100.”<<endl; maxSize = 100; } else maxSize = size; length = 0; list = new elemType[maxSize]; assert(list != NULL); // capture programming error } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  39. Array-Based Lists: ~arrayListType() and arrayListType() template<class elemType> arrayListType<elemType>::~arrayListType() // destructor { delete [] list; } template<class elemType> arrayListType<elemType>::arrayListType(const arrayListType<elemType>& otherList) { maxSize = otherList.maxSize; length = otherList.length; list = new elemType[maxSize]; assert(list != NULL); // capture programming error for(int j = 0; j < length; j++) list[j] = otherList[j]; } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  40. Array-Based Lists: Overloading the Assignment Operator template<class elemType> const arrayListType<elemType>& arrayListType<elemType>::operator= (const arrayListType<elemType>& otherList) { if(this != &otherList) { delete [] list; maxSize = otherList.maxSize; length = otherList.length; list = new elemType[maxSize]; assert(list != NULL); for(inti = 0; i < length; i++) list[i] = otherList.list[i]; } return *this; } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  41. Array-Based Lists: seqSearch() template<class elemType> intarrayListType<elemType>::seqSearch(const elemType& item) { int loc; bool found = false; for(loc = 0; loc < length; loc++) if(list[loc] == item) { found = true; break; } if(found) return loc; else return -1; } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  42. Array-Based Lists: insert() template<class elemType> void arrayListType<elemType>::insert(const elemType& insertItem) { // insert insertItem if it is not in the list int loc; if(length == 0) list[length++] = insertItem; else if(length == maxSize) cout<<“Cannot insert in a full list.”<<endl; else { loc = seqSearch(insertItem); if(loc == -1) list[length++] = insertItem; else cout<<“Duplication is not allowed”<<endl; } } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

  43. Array-Based Lists: remove() template<class elemType> void arrayListType<elemType>::remove(const elemType& removeItem) { int loc; if(length == 0) cout<<“Cannot remove from an empty list”<<endl; else { loc = seqSearch(removeItem); if(loc != -1) removeAt(loc); else cout<<“The item to be deleted is not in the list.”<<endl; } } Dr. Youssef Harrath – University of Bahrain – ITCS 215 – 2010/2011

More Related