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copied!<p>The member variable <code>Circle::r</code> is never set, the local variable <code>r</code> in <code>main()</code> is set via <code>cin</code> but never used.</p> <p>Something like this may be want you want:</p> <pre><code>class Circle { public: Circle(int a_radius) : r(a_radius) {} // function that calculates the area of a circle float circle_area(int r) { area = 3.14 * (r*r); return area; } // end function circle_area void display_msg() { cout << "Area: " << circle_area(r) << endl; } // end function display_msg private: float area; int r; }; // end class Circle int main(void) { int r; cout << "Radius of circle: "; cin >> r; Circle circle_calc(r); circle_calc.display_msg(); } </code></pre> <p>The variable <code>int r</code> declared in <code>main()</code> is not related to the member variable <code>r</code> in class <code>Circle</code>, even though they have the same name: they are two different variables.</p> <p>EDIT:</p> <p>Further refinement of class <code>Circle</code>:</p> <pre><code>class Circle { public: // Constructor. Circle(int a_radius) : r(a_radius) {} // function that calculates the area of a circle float circle_area() { return 3.14 * r * r; } void display_msg() { cout << "Area: " << circle_area() << endl; } private: int r; }; // end class Circle </code></pre> <p>Changes:</p> <ul> <li><code>area</code> does not need to be a member variable (as stated by Fred Larson)</li> <li><code>r</code> is not required to be passed to <code>circle_area()</code> member function as <code>r</code> is a member variable, so <code>circle_area()</code> has access to it</li> </ul>

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