1. CS 215 Final Review
Ismail abumuhfouz
Fall 2014

2. Exam format * true/false (10%) * multiple choices (45%)
* short answers and coding questions (45%)
◮ answering questions
◮ code reading and writing

3. Topics
General topics it would be good to review for each chapter: Definitions and rules.
Technical names of things.
Syntax of C++ constructs.
Meaning of C++ constructs (reading code). System classes, functions, and header files.
Common errors.
Algorithms.

4. Topics Midterm (Chapter 2-5). Vectors & Arrays (Chapter 6).
Pointers (Chapter 7).
Classes (Chapter 9).
Inheritance and polymorphism (Chapter 10).
Recursion (Chapter 11).
Time Complexity (Chapter 12)
Lists, stacks, and queues (Chapter 13).

5. Chapter 2-5 Types and variables Conditionals and loops Functions
◮ int, long, double, char.
◮ Variable naming rule (letter case), scope, address, value.
◮ Variable should be declared and initialized before use.
◮ static cast<int>(myDouble): cast a double to int.
Conditionals and loops
◮ ==, >=, <=
◮ if statement, for loop, while loop, and do-while loop.
Functions
◮ Passing by value, passing by reference (&)
◮ Array parameter is passed by reference by default
◮ Everything else is passed by value by default

6. Chapter 6 Arrays Char arrays Vectors ◮ Declaration of arrays
◮ Array of pointers
◮ Array name is a pointer that points to the first element in this array
◮ int a[5]; What are the types of a, &a, *a, a[2], &(a[2])?
Char arrays
◮ C string: char array.
◮ char* myStr1 = “Hello”; (myStr1 points to a const C string)
◮ char* myStr2 = new char[5]; (myStr2 points to a char array in heap memory)
◮ char myStr3[5]; (myStr3 points to a char array in stack memory)
◮ C++ string, aka string object: std::string strObj(“Hello”);
◮ Converting an string object to C string: strObj.c str();
◮ What is strObj[2] ?
Vectors
◮ push back(), pop back()
◮ vector<int>::iterator it; (vector<int> myVec;)
◮ for (it = myVec.begin(); it != myVec.end(); it++)
◮ for (int i = 0; i < myVec.size(); i++)

7. Pointers and dynamic allocation
Chapter 7
Pointers and dynamic allocation
◮ Declaration of pointers
◮ int myInt = 5; int* myIntPtr1 = &myInt;
◮ int* myIntPtr2 = new int[10];
◮ int* myIntPtr3 = new int;
◮ delete[] myIntPtr2;
◮ delete myIntPtr3;
◮ Should NOT delete myIntPtr1;
◮ Array-pointer duality: a[i] = *(a + i)
◮ Pointer arithmetic: + 1 goes to next element in an array.
Common errors
◮ Deferencing uninitialized / NULL pointer
◮ Memory leaks (didn’t free something).
◮ Dangling pointer (using already-deleted memory).
◮ Bounds error (going past the allocated array).
◮ Wrong deletion operator.

8. Chapter 9 Encapsulation: separating interface from implementation.
◮ All access to your class goes through the interface.
⋆ The public member functions (methods).
◮ Member variables (data) are private.
⋆ Only accessible by the methods.
A class describes a set of objects with the same behavior.
◮ A class is a type.
◮ An object is a thing of that type.
◮ You use an object by calling its methods.
Constructors
◮ Initialize an object’s private data.
◮ Same name as the class.
◮ When does a constructor get called?
◮ Difference between default constructor and overloaded constructor?
Destructors
◮ Name is class name with a tilde before it: ∼className().
◮ No return type, no parameters.
◮ Frees any data allocated in the class.
◮ Automatically called when the object ceases to exist.
Xiwei (Jeffrey) Wang (UK CS)
CS 215 Final Review

9. Chapter 10 Inheritance Inherited methods
◮ Implements the “is-a” relationship. What about aggregation? (“has- a”).
◮ Derived class inherits from the base class.
◮ C++ syntax: class Car : public Vehicle {...};.
◮ The derived class has all the members of the base class, plus any additional members declared in the derived class.
◮ Base-class private data is not directly accessible.
⋆ Use the base-class constructor to initialize the data:
Derived::Derived(...) : Base(...) {...}
⋆ Use accessors to get their values.
Inherited methods
◮ Methods are inherited: can call a base-class method on a derived- class object.
◮ You can override a method by redefining it in the derived class.
⋆ Can call the base class version:
BaseClass ::method();.

10. Chapter 10 Slicing and polymorphism
◮ Putting a derived class object into a base-class variable slices off the derived parts.
⋆ This is usually not what you want.
◮ Base-class pointers and references can safely point to derived objects, without slicing.
⋆ Static type: declared type of the pointer (Person *)
⋆ Dynamic type: what it actually points to (Employee *)
⋆ Polymorphism is when these are different.
virtual functions and abstract classes
◮ If you want to use polymorphism, you should declare the methods (the ones that will be overridden in derived classes) in based class as virtual.
◮ If a class contains at least one pure virtual function, it is an abstract class.
◮ You cannot instantiate an abstract class (creating objects of this class)

11. Chapter 11 Recursion: a function calling itself.
◮ The idea: solve a hard problem by first solving an easier version of the same problem
◮ which you solve by finding an even easier version
◮ until the problem is so easy you can solve it right away.
Two components of a recursive function
◮ There must be special cases to handle the simplest tasks directly so that the function will stop calling itself. (Base case)
◮ Every recursive call must simplify the task in some way. (Recursive call )

12. Chapter 11 Example recursive definitions: Avoiding infinite recursion:
◮ Factorial: Base case: n <= 1 → n! = 1; General case: n > 1
Recursive formula: n! = (n − 1)! ∗ n
◮ Fibonacci: Base cases: n <= 1 → F (0) = F (1) = 1; General case: n > 1
Recursive formula: F (n) = F (n − 1) + F (n − 2)
◮ Merge sort: Base case: a one-element array is already sorted. Recursive call: cut in half, merge sort each half, then merge.
Avoiding infinite recursion:
◮ Must check the base case first.
◮ No recursion in the base case!
◮ And the recursive call(s) must bring you closer to the base case.
Mutual recursion: A calls B, B calls C, C calls A.

13. Chapter 12 Run-time complexity
◮ How does the time taken depend on the input size?
◮ Order of complexity: big O notation.
⋆ Calculate the number of operations performed.
⋆ Take only the fastest-growing term (highest exponent).
⋆ Remove any constant factors.
⋆ 3n2 + 6n becomes O(n2).
⋆ O(1) < O(logn) < O(n) < O(nlogn) < O(n2) < O(n3) < O(2n )

14. Chapter 13 Stacks Queues Linked list
◮ A stack lets you insert and remove elements at one end only.
◮ Stack is a LIFO (Last-In, First-Out) data structure.
Queues
◮ A queue lets you add items to one end of the queue (the back) and remove them from the other end of the queue (the front).
◮ Queue is a FIFO (First-In, First-Out) data structure.
Linked list
◮ Linked list is a data structure that supports efficient addition and removal of elements in the middle of a sequence.
◮ A typical doubly linked list node has three fields: data, previous pointer, next pointer.
◮ A typical singly linked list node has two fields: data, and next pointer.
◮ STL linked list: std::list<string> myList;
◮ Iterator: list<string>::iterator it;