```/*
* Copyright 2011 Steven Gribble
*
*  This file is the solution to an exercise problem posed during
*  one of the UW CSE 333 lectures (333exercises).
*
*  333exercises is free software: you can redistribute it and/or modify
*  it under the terms of the GNU General Public License as published by
*  the Free Software Foundation, either version 3 of the License, or
*  (at your option) any later version.
*
*  333exercises is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*  GNU General Public License for more details.
*
*  You should have received a copy of the GNU General Public License
*  along with 333exercises.  If not, see <http://www.gnu.org/licenses/>.
*/

// Lecture 15 exercise 1

#include <utility>   // for std::pair
#include <string>    // for std::string
#include <iostream>  // for std::ostream

#ifndef _LEC15_EX1_SHAPE_H_
#define _LEC15_EX1_SHAPE_H_

const double PI = 3.141592653589793238462643383279502884;

// A "Shape" is an abstract class representing some kind of
// two-dimensional shape.
class Shape {
public:
Shape() { }
// Make the destructor virtual; this is good hygiene, since it
// guarantees that the full class hierarchy below Shape has virtual
// destructors.
virtual ~Shape() { }

// Return the centroid of the shape.  A centroid is a pair, where
// .first() is the x-coordinate and .second is the y-coordinate.
virtual std::pair<double, double> Centroid() const = 0;

// Return the area of the shape.
virtual double Area() const = 0;

// Move the shape by adding "delta" to the shape.
virtual void Move(const std::pair<double, double> &delta) = 0;

// Return a string with some pretty-printed shape details.
virtual std::string Print() const = 0;
};

std::ostream &operator<<(std::ostream &out,
const std::pair<double,double> &p);

#endif  // _LEC15_EX1_SHAPE_H_
```