1. CS114-009 Class 19 Today  Practice with classes Announcements  Turn in algorithm for Project 5 in class today  Project 5 due 11/11 by midnight – e-mail to vrbsky@cs.ua.edu vrbsky@cs.ua.edu  Make sure you have read Section 10.2 pp. 540-572

2. Review – creating a class Our class  LARGE INTEGERS  Normal integer can only hold up to 2 billion  Want to be able to hold a number with up to 100 digits in it Declaration class INT { // Attributes // items needed to // represent the data public: // Methods // constructors // basic arithmetic (+, –) // input and output };

3. Sample Class (for large ints) Data representation  100 digits  Sign (positive or negative) Constructors  Two constructors  Default INT a, b, c[10];  Construct from an integer INT a(-37), b=89, c[2]={12,34}; Other operations  Addition  Read and Write Last four methods are better  Use actual + and – operators  Use actual > operators Friends (for I/O) Overload > for INT  Will focus on those in CS 124 class INT { int digits[100]; char sign; public: INT( ); INT(int num); void Add(INT);// x.Add(y); void Read( );// x.Read(); void Write( );// x.Write(); INT& operator + (const INT& a); INT& operator - (const INT& a); friend ostream& operator<< (ostream&, const INT&); friend istream& operator>> (istream&, INT&); };

4. class INT { int digits[100]; char sign; public: INT( ); void Read( ); void Write( ); void Add( INT ); }; Try to get this version working int main( ) { INT a, b; a.Read( ); b.Read( ); a.Write( ); cout << endl; b.Write( ); cout << endl; a.Add(b); a.Write( ); cout << endl; return 0; }

5. “Dot” notation We’ve seen this, but haven’t discussed. Classes we’ve worked with: cin, cout, string  cin.eof()// End of File?  string num; num.length();// length of a string  num.at(i);// character in num  cout.setf(ios::fixed)// set the output format The ‘dot’ is a way of calling a function for that object.  s1.length(); s2.length(); s3.length(); // different objects, different lengths

6. Code for Constructor INT::INT( ) { for (int a=0;a<100;a++) digits[a] = 0; sign = 'p'; } System automatically calls constructor whenever a variable of this type is declared Constructor initializes all digits to zero and the sign to ‘p’  ‘n’ represents negative

7. Code for Read & Write void INT::Write() { int a = 0; if (sign == 'n') cout << '-'; while (a < 100) cout << digits[a++]; } void INT::Read() { string num; cin >> num; if (num.at(0) == '-') sign = 'n'; if (num.at(0) == '+') sign = 'p'; int s = 0; if ( !isdigit( num.at(0) ) ) s = 1; int loc = 100 – (num.length() - s); for (int a=s; a<num.length(); a++) digits[loc++] = num.at(a) – '0'; } Write simply prints out a leading sign (if the number is negative) followed by 100 digits Read inputs the variable into a string (temporarily) and then extracts from the string into the array of digits

8. Code for Add method void INT::Add(INT num) { if (num.sign == 'n' || sign == 'n') cout << “not done" << endl; else { int a, carry = 0, total; for (a=99; a>=0; a--) { total = digits[a] + num.digits[a] + carry; if (total > 9) carry = 1; else carry = 0; digits[a] = total % 10; } Syntax  INT a, b;  a.Add(b); Only adds numbers if both are positive Ignores overflow (result greater than 100 digits)

9. Class Exercise The class we have started is on our web page: Big_INT.cpp Big_INT.cpp Download this program, then compile and run  Modify Write( ) so that it does not print leading zeros in the number  Modify Add( ) so that it is also capable of adding two negative numbers  Modify Read( ) so that it erases the previous contents of the object

10. Addition to Class Exercise:  Modify Add( ) so that it is also capable of adding two negative numbers Consider how “Add()” works. It’s called this way: INT a, b; // read values… a.Add(b); // adds the value of b to a

11. void INT::Add(INT num) if (sign == ‘n’ || num.sign == ‘n’) … What’s the difference between “sign” and “num.sign”? We’re adding two objects.  One is the parameter “num”.  The other one is “this” object. Call: a.Add(b) adds ‘b’ to ‘a’. a: 42b: 13

12. void INT::Add(INT num) if (sign == ‘n’ || num.sign == ‘n’) … Which one is “sign”? Which one is “num.sign”? a: 42b: 13 a.Add(b) ;

13. Every Class needs… Functions that give you the (private) values Functions that let you change the values We call them:  Accessors (or “getters”) Usually called “getValue()” (for each “Value” attribute)  Mutators (of “setters”) Usually called “setValue(x)” Other language:  Class data members are called “attributes”  Class functions are called “methods”

14. The Car Class Download the file cars.cpp from our class web pagecars.cpp What is the constructor of the Car class?  What does this constructor do, in terms of setting attributes? Identify the accessors  Better known as “getter” methods Identify the mutators  Better known as “setter” methods Identify the other methods. What do they do? Could the functions outside of the Cars class be rewritten as methods for the Cars class?

15. Class Exercise Write the definitions to the following methods, whose prototypes you’ll find on cars.cpp setCarInfo() – set a car’s information, given the make, model, type, doors, quantity of the car in stock, cylinder engine, and liters of the engine load() – reads in information from the file cars.txt, and uses setCarInfo() to set the information for an instance of car  Data for each car is on one line. The order of the data: Make, Model, Type, Doors, Liters, Cylinders, Quantity

16. Class exercise Download the file box.cpp from our class web pagebox.cpp Write the definitions to the following methods, whose prototypes you’ll find in box.cpp  volume() – given the height, width, and length of a box, return its volume  compare() – compares the volume of a box to another box; returns true if the volumes of the 2 boxes are equivalent, otherwise returns false. Insert lines of code into main( ) as indicated to utilize the appropriate member function. (see comments in box.cpp)

17. End of Class 19