Modify the Vector class header and implementation files (Listings 11.13 and 11.14) so that the magnitude and angle are no longer stored as data components. Instead, they should be calculated on demand when the magval() and angval() methods are called.You should leave the public interface unchanged (the same public methods with the same arguments) but alter the private section, including some of the private method and the method implementations.Test the modified version with Listing 11.15, which should be left unchanged because the public interface of the Vector class is unchanged.

Notice that the four functions in Listing 11.13 that report component values are defined in the class declaration. This automatically makes them inline functions. The fact that these functions are so short makes them excellent candidates for inlining. None of them should alter object data, so they are declared using the const modifier. As you may recall from Chapter 10, this is the syntax for declaring a function that doesn’t modify the object it implicitly accesses.
Listing 11.14 shows all the methods and friend functions declared in Listing 11.13.
The listing uses the open nature of namespaces to add the method definitions to the VECTOR namespace. Note how the constructor functions and the reset() function each set both the rectangular and the polar representations of the vector. Thus, either set of values is available immediately without further calculation, should you need them. Also as mentioned in Chapter 4,“Compound Types,” and Chapter 7, C++’s built-in math functions use angles in radians, so the functions build conversion to and from degrees into the methods. The Vector class implementation hides such things as converting from polar coordinates to rectangular coordinates or converting radians to degrees from the user.

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Listing 11.13 vect.h // vect.h -- Vector class with <<, mode state #ifndef VECTOR_H_ #define VECTOR_H__ #include namespace VECTOR { class Vector { public: enum Mode {RECT, POL}; // RECT for rectangular, POL for Polar modes private: double x; double y; double mag; double ang; Mode mode; // private methods for setting values void set_mag(); void set_ang(); void set_x(); void set_y(); // horizontal value // vertical value // length of vector // direction of vector in degrees // RECT or POL public: Vector (); Vector (double n1, double n2, Mode form = RECT); void reset (double nl, double n2, Mode form = RECT); -Vector (); double xval() const {return x; } double yval() const {return y;} double magval() const {return mag;} double angval() const {return ang;} void polar_mode (); void rect_mode (); // operator overloading Vector operator+(const Vector & b) Vector operator- (const Vector & b) Vector operator- () const; Vector operator* (double n) const; // friends // report x value // report y value // report magnitude // report angle // set mode to POL // set mode to RECT }; } // end namespace VECTOR #endif const; const; friend Vector operator* (double n, const Vector & a); friend std::ostream & operator<<(std::ostream& os, const Vector & v);