2020春_c_19信网一些较好籍savitch_ch_09.pptVIP

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Creating Dynamic Arrays Normal arrays require that the programmer determine the size of the array when the programis written What if the programmer estimates too large? Memory is wasted What if the programmer estimates too small? The program may not work in some situations Dynamic arrays can be created with just the right size while the program is running Slide 9- * Creating Dynamic Arrays Dynamic arrays are created using the new operator Example: To create an array of 10 elements of  type double: typedef double* DoublePtr; DoublePtr d; d = new double[10];  d can now be used as if it were an ordinary array! Slide 9- * This could be an integer variable! Dynamic Arrays (cont.) Pointer variable d is a pointer to d[0] When finished with the array, it should be deleted to return memory to the freestore Example: delete [ ] d; The brackets tell C++ a dynamic array is being deleted so it must check the size to know how many indexed variables to remove Forgetting the brackets, is not legal, but would tell the computer to remove only one variable Slide 9- * Display 9.6 (1) Display 9.6 (2) Pointer Arithmetic (Optional) Arithmetic can be performed on the addresses contained in pointers Using the dynamic array of doubles, d, declared previously, recall that d points to d[0] The expression d+1 evaluates to the address of d[1] and d+2 evaluates to the address of d[2] Notice that adding one adds enough bytes for onevariable of the type stored in the array Slide 9- * Pointer Arthmetic Operations You can add and subtract with pointers The ++ and - - operators can be used Two pointers of the same type can be subtracted to obtain the number of ind