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(C++) Exercise #6: refactoring quadratic solver


Difficulty: 2/10

Date added: 21th of July 2008


In this exercise you must refactor a class that is given as an example in reference [1]. You will learn how to think to correctly refactor a class and that literature does not always set a good examples.


A quadratic equation is an equation in the form 'ax2 + bx + c = 0'. For which x or x's is this true? The number of solutions this equation has is determined by the discrimant: D = b2 - 4ac. If D is smaller then zero, the equation has no solutions. If D equals zero, the solution to the equation is x = -b/2a. If D is bigger then zero, the solutions are x = (-b-sqrt(D)) / (2a) and x = (-b+sqrt(D)) / (2a).


Below of a piece of code (from [1]) demonstrating a class to solve a quadratic equation. Can you refactor this class to follow good class design, member function design, function design and good thinking?


#include <cmath>

using namespace std;

class Qs
  void coeff(double aa, double bb, double cc)
    a = aa;
    b = bb;
    c = cc;
  bool solve()
    double D = b * b - 4 * a * c;
    if (a == 0 || D < 0) return false;
    double rD = sqrt(D);
    x1 = (-b + rD)/(2 * a);
    x2 = (-b - rD)/(2 * a);
    return true;
  double root1() const { return x1; }
  double root2() const { return x2; }

  double a,b,c,x1,x2;






View the answer of this exercise.








  1. Leen Ammeraal. C++ (6th edition). ISBN: 90-395-1935-8. 2001






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