Discussion 10: Exam 2 Review

Transcription

1 EECS 183 Ryan Cesiel

2 Exam Tips: Preparing for the Exam Focus your studying: focus on what you don t know and the most important topics (generally the ones we have spent the most time on) Skimming lecture slides / iclicker questions is a great way to gauge this Learn from what you missed on exam 1: was FR hard or MC? What types of questions? Old exams: recent exam 2s (and 3s); no Python questions Your projects: review projects 3 and 4; identify any code you re uncomfortable with or your partner wrote and make sure you understand it

3 Taking the Exam 3 x 5 handwritten notecard! Ideas: ifstream/ofstream examples, examples of classes, creating class instances and using them, constructors, testing examples If you re stuck, look around the exam at other questions to see if code jogs your memory Identify what section you feel most comfortable starting (FR or MC) Skip longer questions and come back to them

4 Key Notes on Arrays EXAMPLE 1 Always pass-by-reference int grid[3][3];... my_func(grid); Only the array name is passed to a function (example 1) EXAMPLE 2 The cols must be specified in a 2D array (example 2) Omitting rows is only valid as a parameter (example 3) int grid[3][3]; int grid[3][]; int grid[][3] = {...}; Practice problems: previous exams, project 3 EXAMPLE 1 int func(int arr[][size]);

5 Stream States Managing the stream: You must explicitly check the stream state; i.e. you will not be notified when something goes wrong Think project 4 and detecting what form Triangle/Rectangle input was in Reading the stream while(cin >> x) while(cin.good()) NOT while(!cin.eof())! Note: see openfile( ) function from lecture

6 File Stream Example 1: Reading/Writing With Existing File #include <fstream> using namespace std; int main() { string name; ifstream read; The file filename.txt contains Ryan read.open("filename.txt"); read >> name; read.close(); Assigns the string Ryan to the variable name return 0; }

7 File Stream Example 2: Reading/Writing With Existing File #include <fstream> using namespace std; int main() { The file filename.txt contains Ryan string name = "Cesiel"; ofstream write; write.open("filename.txt"); Writes the string Cesiel to the file filename.txt } write << name; write.close(); return 0; What does filename.txt contain?

8 File Stream Example 2: Reading/Writing With Existing File #include <fstream> using namespace std; int main() { The file filename.txt contains Ryan string name = "Cesiel"; ofstream write; write.open("filename.txt"); Writes the string Cesiel to the file filename.txt } write << name; write.close(); return 0; What does filename.txt contain? Only Cesiel

9 Key Notes on File Streams Output will overwrite existing data in file Remember: Input opening will fail if the file does not exist! Output will open new file if one does that name Output = ofstream Input = ifstream does not exist already If output file doesn t exist, creates it in the same directory that your project is in

10 Key Note on.clear() Must manually fix streams: use.clear() on cin or the file stream to reset flags However, this does not move past the bad input! It will be in the same location. Think loadfile and read functions in project 4. loadfile: if line was incorrect, why was getline necessary? Triangle::read or Rectangle::read: differences for short vs long forms? string garbage; string garbage; Try for int a, b; int a, b; Input: cin >> a >> b; vs. cin >> a >> b; yourself cin.clear(); cin.clear(); 1 x 5 cin >> b; cin >> garbage >> b;

11 File Stream Practice Exams F15 Exam 2 FR Q4, W14 Exam 3 FR Q3 hangarreport(), F14 Exam 2 FR Q13 Numerous MCs Rewrite project 4 loadfile, Triangle::read or Rectangle::read Ryan s discussions slides Exam MC questions and related questions in discussions 7, 9 and 10 (today) Next slide (credit: Maxim Aleksa)

12 F15 Exam 2 FR Q4

13 File Stream Practice Problems Write a program that asks user for a filename and prints the contents of that file. Write a program that asks user for two filenames and copies the contents (each line) of the first file into the second file (new or overwritten). Write a program that asks user for two filenames and copies each line of the first file into the second file (new or overwritten), in reverse order. Write a program that asks the user for a filename and then prints the longest word in that file.

14 Classes terms and vocabulary Instance/Object: a declared variable of type class ex: Student ryan; we say the variable ryan is an instance or object of type Student Constructor: a special member function automatically called when you create a class; the constructor was called in the instance example above Syntax: Student::Student() { implementation } (Note: no return type) Member variables/functions: variables or functions that belong to (inside) the class Private/Public: public means we can access outside the class; private means we can t getters/setters: Functions to get or set private member variables

15 const int MAX_INGREDIENTS = 20; class ChipotleBurrito { public: ChipotleBurrito(); ChipotleBurrito(string meattype); // Determines whether a certain ingredient is already // included in this burrito or not bool isingredientpresent(string ingredientname); // Adds the given ingredient to the burrito, if it is not // already present. If it is already present, this // function does nothing. void addingredient(string ingredientname); private: string ingredientnames[max_ingredients]; int numingredients; };

16 Chipotle Problem Ctn. Assume, the Chipotle class was successfully implemented. 1. Create an instance of Chipotle called burrito with chicken in it 2. Add guacamole to burrito 3. Test to make sure the guacamole was successfully added

17 Chipotle Problem Ctn. Assume, the Chipotle class was successfully implemented. 1. Create an instance of Chipotle called burrito with chicken in it 2. Add guacamole to burrito 3. Test to make sure the guacamole was successfully added ChipotleBurrito burrito("chicken"); burrito.addingredient("guacamole"); if (!burrito.isingredientpresent("guacamole")) { cout << "error adding ingredient!" << endl; }

18 Key Notes on Classes Member functions and variables are private by default Constructors are implicitly called when an instance is created (i.e. Rectangle r1;) Constructors have no return type and share the same name as the class The scope resolution operator (::) designates the class the member function belongs to (see Project 4 *.cpp files)

19 Class Practice Exams F13 Exam 3 FR Q4, Fall 2014 Exam 2 FR Q14 and Q15, W14 FR Q3, Numerous MCs Project 4 constructors, getters, setters, etc Ryan s discussions slides Exam MC questions and related questions in discussions 8, 9 and 10 (today)

20 W14 Exam 3 FR Q3 default constructor, non-default constructor, dockship, findship, hangarreport