Exercise · Classes and OOP · lesson 12 of 13

Exercise: shapes with a virtual area

The abstract class Shape with the method virtual double area() const = 0 is already declared. Complete the classes Circle and Rect derived from it; add the fields yourself. Circle(double radius) is a circle of radius radius, and Rect(double w, double h) is a rectangle with sides w and h.

Also write the function double total_area(const std::vector<const Shape*>& shapes), which returns the sum of the areas of all the shapes. Take π from the constant kPi, which the file already defines.

Circle(1.0).area() → kPi
Rect(2.0, 3.5).area() → 7.0
total_area({&c, &r}) for Circle c(1.0) and Rect r(2.0, 3.0) → kPi + 6.0

Constraints: the sizes are non-negative; the same shape may appear in the vector several times; for an empty vector, total_area returns 0.

shapes.cpp — cpp

cpp · 34 lines

#include <vector>

constexpr double kPi = 3.141592653589793;

class Shape {
public:
    virtual ~Shape() {}
    virtual double area() const = 0;
};

class Circle : public Shape {
public:
    Circle(double radius) {
    }

    double area() const override {
        return -1;
    }
};

class Rect : public Shape {
public:
    Rect(double w, double h) {
    }

    double area() const override {
        return -1;
    }
};

double total_area(const std::vector<const Shape*>& shapes) {
    return -1;
}

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