Lecture 17OutlineDestructorCopy ConstructorAssignment OperatorRules for Dynamic ClassesStatic Multi-dimensional ArraysDynamic Multi-dimensional Array 1Dynamic Multi-dimensional Array 2Dynamic Multi-dimensional Array 3Dynamic 2D AllocationDynamic 2D AccessDynamic 2D DeallocationIn-class ExerciseFriday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 1Lecture 17No code files for todayReminder: Project 3 due today. Homework 5 (!) due on Monday.Questions?Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 2OutlineRules for dynamic classesDestructor, copy constructor, assignment operatorStatic multi-dimensional arraysDynamic multi-dimensional arraysFriday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 3DestructorPrototype is ~ClassName();Automatically called before an object is destroyed.Deallocates the dynamically-allocated data in the opposite order of construction.Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 4Copy ConstructorPrototype is: ClassName(const ClassName & source);Automatically called to create a value parameter copy, a return value copy, or a variable with initialization.Dynamically-allocates a new data structure to hold a copy of the dynamic data of the source.Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 5Assignment OperatorA member function. Prototype isvoid operator=(const ClassName & source);Called for assignmentsClassName obj1, obj2;:obj1 = obj2;Must check for self-assignment. Deallocates the dynamically-allocated data in the opposite order of construction, then dynamically-allocates a new data structure to hold a copy of the dynamic data of the source.Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 6Rules for Dynamic ClassesAt least one attribute is a pointer variable.Member functions allocate and release memory as needed.The class will have custom destructor, copy constructor, and assignment (operator=) functions. Note: without a destructor, the class will create garbage, but will otherwise be correct. Without the copy constructor or the assignment operator, the class will be incorrect.Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 7Static Multi-dimensional Arrayint array2D[NUM_ROWS][NUM_COLS];[0][0] [1] [2] [3] ...[NUM_COLS-1][1][2][3]:[NUM_ROWS-1]Access: array2D[i][j]Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 8Dynamic Multi-dimensional ArrayCannot allocate a multi-dimensional array directly, since the new operator can create only a one-dimensional array.But we can think of a two-dimensional array as a one-dimensional array with one-dimensional array elements.Applying this idea to dynamically-allocated arrays, we get a pointer to an array of pointers to arrays of integer.Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 9Dynamic Multi-dimensional Array[2][3][0][1]::[NUM_ROWS-1]...[0] [1] [2] [3] ...[NUM_COLS-1]............array2DPtrFriday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 10Dynamic Multi-dimensional ArrayWhat is the type of array2DPtr? It is a pointer to an array of pointers to integer arrays.The type of the outer array elements is int *.So the type of a pointer to the outer array is int **.How to allocate? Since dynamic, can ask the user for the dimensions, numRows and numCols. First allocate the outer array, then allocate the individual rows.Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 11Dynamic 2D AllocationTo allocate the outer array say:int **array2DPtr = new int *[numRows];To create each individual row, need to allocate an integer array and make an outer element point to it.for (int i = 0; i < numRows; i++) array2DPtr[i] = new int [numCols];type of the elements in each rowtype of the elements of the outer arrayFriday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 12Dynamic 2D AccessHow to access an element of this data structure? Indexing is the same as with a static multi-dimensional array: array2DPtr[i][j]Why does this work?*(array2DPtr+i) => array2DPtr[i] => address of rowarray2DPtr[i]+j => address of an element*(array2DPtr[i]+j) => array2DPtr[i][j]Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 13Dynamic 2D DeallocationDeallocation needs to be done in the opposite order of allocation. Delete the rows first, then the outer array.// Delete the rows firstfor (int i = 0; i < numRows; i++) delete [] array2DPtr[i];// Delete the outer arraydelete [] array2DPtr;Friday, October 1 CS 215 Fundamentals of Programming II - Lecture 17 14In-class ExerciseOn a piece of paper, answer the following questions:1. Write a declaration for a pointer variable array3DPtr that will point to a dynamic 3D boolean array.2. Write the code for allocating storage for numRows x numCols x numDepth elements with array3DPtr pointing to the outer array.3. Write the code to initialize the storage allocated in (2) to be true if the sum of the indexes of an element is even and false if the sum of the indexes of an element is odd. That is, element array3DPtr[i][j] is true if i+j is even, etc.4. Write the code for deallocating the storage allocated in
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