This Weeks Topics: Pointers continued

1. This Weeks Topics: Pointers (continued) Modify C-String through a function call Dynamic variable new keyword and delete keyword Arrays and pointers Pointer arithmetic Dynamic array Size not specified at programming time Determined while program running

2. Modify C-String in a function call or exchange the value of two C-Strings Pass by value of the c-string (char *)? Won�t� work Pass by the reference of the c-string (char * &)? Yes, it works Pass by pointer to the c-string (char **)? Yes, it works How to implement?

3. The new Operator Since pointers can refer to variables� No "real" need to have a standard variable Can dynamically allocate variables Operator new creates variables int * p1; p1 = new int; Creates new "nameless" variable, andassigns p1 to "point to" it Can access with *p1 Use just like ordinary variable

4. Basic Pointer Manipulations Example: Display 10.2 Basic Pointer Manipulations (1 of 2)

5. Basic Pointer Manipulations Example: Display 10.2 Basic Pointer Manipulations (2 of 2)

6. Memory Management Heap Reserved for dynamically-allocated variables All new dynamic variables consume heap memory If too many ? could use all heap memory Problem: future "new" operations will fail if heap is "full� Resolution: use delete operator to de-allocate spaces

7. delete Operator De-allocate dynamic memory When no longer needed Returns memory to heap Example:int *p;p = new int;� //Some processing�delete p; De-allocates dynamic memory "pointed to bypointer p" Literally "destroys" memory

8. Dynamic and Regular Variables Dynamic variables Created with new operator; destroyed with delete operator Created and destroyed while program runs Local variables Declared within function definition Not dynamic Created when function is called Destroyed when function call completes

9. Recall: Array Variables Arrays stored in memory addresses sequentially Array variable "refers to" first indexed variable So array variable is a kind of pointer variable!

10. Array Variables ? Pointers Example:int a[10];int * p; and p are pointer variables Can perform assignments:p = a; // Legal. p now points where a points To first indexed variable of array a a = p; // ILLEGAL! Array pointer is CONSTANT pointer!

11. Pointer Arithmetic Can perform arithmetic on pointers "Address" arithmetic Example:double f[4] = {1.1, 2.2, 3.3, 4.4};double * d = f; d contains address of d[0] d + 1 evaluates to address of d[1] d + 2 evaluates to address of d[2] Equates to "address" at these locations

12. Alternative Array Manipulation Use pointer arithmetic! �Step through� array without indexing:for (int i = 0; i < arraySize; i++) cout << *(d + i) << " " ; Equivalent to:for (int i = 0; i < arraySize; i++) cout << d[i] << " " ;

13. Array and Pointers

14. Array and Pointers (continued)

15. Dynamic Arrays Array limitations Must specify size first May not know until program runs! Must "estimate" maximum size needed Sometimes OK, sometimes not "Wastes" memory Dynamic arrays Can determine size at runtime

16. Creating Dynamic Arrays Use new operator Dynamically allocate with pointer variable Treat like standard arrays Example:double *d;d = new double[10]; //Size in brackets, can be variable Creates dynamically allocated array variable d,with ten elements, base type double

17. Deleting Dynamic Arrays Allocated dynamically at run-time So should be destroyed at run-time Simple again. Recall Example:double * d = new double[10];� //Processingdelete [] d; De-allocates all memory for dynamic array Brackets indicate "array" is there

18. Multidimensional Dynamic Arrays Recall: "arrays of arrays" int **m = new int *[3]; Creates array of three pointers Make each allocate array of 4 ints for (int i = 0; i < 3; i++) m[i] = new int[4]; Results in three-by-four dynamic array!

19. Multidimensional Dynamic Arrays: De-allocate memories In the reverse order allocating spaces for (int i = 0; i < 3; i++) delete [] m[i]; delete[] m;