Download Introduction to Computer science - Programming Abstractions, Lecture 12 and more Lecture notes Programming Abstractions in PDF only on Docsity! Admin Today’s topics • More pointers, recursive data, linked lists Reading • linked lists Ch 9.5(sort of), handout #21 • algorithms, big O Ch 7 (next) Assign 3 due, Assign 4 out • Joy poll? • Boggle awesomeness • Paper copy delinquency Lecture #12 Simple pointer operations int main() { int num; int *p, *q; p = new int; *p = 10; q = new int; *q = *p; q = p; delete p; delete q; // bad idea, q already deleted! q = NULL; // NULL is zero pointer, used as sentinel value Pointer basics Pointers are distinguished by type of pointee • Type double* not same as int* Pointers are uninitialized until assigned • Dereferencing a uninitialized pointer is bad news Dynamic allocation via new • Operator new allocates memory from heap, returns address Manual deallocation via delete • Forgetting to delete means memory is orphaned • Accessing deleted memory has unpredictable consequences Pointers and dynamic arrays int main() { int *arr = new int[10]; for (int i = 0; i < 10; i++) arr[i] = i; delete[] arr; // delete[] if allocated with new[] Raw arrays can be trouble • Manually allocated and deallocated • Don't know their length • No bounds-checking • Cannot easily change size once allocated • Allocate new space, copy over, update pointer Vector uses array behind scenes, but hides issues Use of pointers Axess database A course has pointers to enrolled students • Allocate studentT record in heap for new student • Each course student enrolls in stores pointer to record • Saves space by not repeating student information • If student gets new phone number, change in one place only! struct studentT { string first, last; string address, phone; }; struct courseT { string dept, name; Vector<studentT *> students; }; Recursive data Recursion applied to data • Self-referential, self-similar • Within itself, data has smaller version repeated Examples • Matroshka dolls • Nesting boxes • Onions • Structure containing pointer to same structure A recursive struct struct Entry { string name, address, phone; Entry *next; }; Each entry points to another Entry! Wired together, you get a linked list! name address phone next Rein 123 Pine 555-0123 Kalev 204 Elm 555-8765 Mati 89 Oak 555-9425 Creating a node Entry *GetNewEntry() { cout << "Enter name (ENTER to quit):"; string name = GetLine(); if (name == "") return NULL; Entry *newOne = new Entry; newOne->name = name; cout << "Enter address: "; newOne->address = GetLine(); cout << "Enter phone: "; newOne->phone = GetLine(); newOne->next = NULL; // no one follows return newOne; }
