Project 6 – Building a Class

B Smith: Took 50 minutes. Score 3. Elaborated extensively on parts. B Smith: Cover during Recitation Project 6 – Building a Class

Overview • Example using Point Class • Implementation • Initialization Lists • Use of ostringstream (using toString() ) • Finding the greatest common divisor (gcd) • Euclidean Algorithm • Copy Constructor • Assignment Operator

A Point Class • A point in the cartesian plane can be represented by a Class

B Smith: discuss use of const! Students use this example as the template for the project! Careful with the assignment operator and the copy constructor. Interface for the Point Class class Point { public: Point(double=0.0,double=0.0); // default constructor Point(const Point&); // copy constructor ~Point(); // destructor Point& operator=(const Point&); // assignment operator double getX() const; double getY() const; string toString() const; private: double _x, _y; };

Test Driver for the Point Class int main() { Point p0; // invokes default constructor cout << "p0 = " << p0.toString() << "\n"; Point p1(5,-2); // invokes default constructor cout << "p1 = " << p1.toString() << "\n"; Point p2=p1; // invokes copy constructor cout << "p2 = " << p2.toString() << "\n"; p0 = p1; // invokes assignment operator cout << "p0 = " << p0.toString() << "\n"; cout << "p0.getX() = " << p0.getX() << "\n"; cout << "p0.getY() = " << p0.getY() << "\n"; }

Point Class Implementation #include <sstream> // defines ostringstream class #include "Point.h" // defines Point class Point::Point(double x, double y) : _x(x), _y(y) { } Point::Point(const Point& p) : _x(p._x), _y(p._y) { } Point::~Point() { } Point& Point::operator=(const Point& p) { _x = p._x; _y = p._y; return *this; } double Point::getX() const { return _x; } double Point::getY() const { return _y; } string Point::toString() const { ostringstream output; output << "(" << _x << "," << _y << ")"; return output.str(); }

What’s New • Initialization Lists • Use of ostringstream.

Initialization Lists Point::Point(double x, double y) : _x(x), _y(y) { } Point::Point(double x, double y) { _x = x; _y = y; }

Stream Classes for Strings • A mechanism that can be used to read from strings or write to strings • String streams provide a buffer • This buffer/string can be manipulated with special functions

ostringstream • The toString() function uses a string stream to accumulate its output • ostringstream objects can use a member function called str(), which returns the buffer as a string string Point::toString() const { ostringstream output; output << "(" << _x << "," << _y << ")"; return output.str(); }

Euclidean Algorithm • Given nonnegative integers m and n, this algorithm finds their greatest common divisor • for gcd(m,n) • n = 0? Then stop with m as the answer. Otherwise: • r (m mod n) • mn • nr • go to step 1.

B Smith: This is not a good explanation! Euclidean Example gcd(40902, 24140) = gcd(24140, 16762) = gcd(16762, 7378) = gcd(7378, 2006)= gcd(2006, 1360) = gcd(1360,646)= gcd(646, 68) = gcd(68, 34)= gcd(34,0)= 34

Euclidean Implementation long gcd(long m, long n) {long r; while( n > 0 ) { r = m%n; m = n; n = r; } return m; }

gcd() client // client/driver function for gcd() int main() { int a = 24140, b = 16762; int c; c = gcd(a,b); cout << "The gcd of a and b is: " << c ; return 0; }

Reducing to lowest terms: norm() • Think about this one. It probably will require use of the gcd(), as well as some logical checks

Project 6 – Building a Class