private static void DisplayExample(Polynomial first, Polynomial second, Polynomial added, Polynomial subtracted, Polynomial multiplied)
        {
            StringBuilder print  = new StringBuilder();
            string        border = new string('-', 60);

            print.AppendLine("Problem 11. Adding polynomials \nWrite a method that adds two polynomials. \nRepresent them as arrays of their coefficients.")
            .AppendLine("Problem 12. Subtracting polynomials \nExtend the previous program to support also subtraction and multiplication of polynomials.");

            // print
            print.AppendLine("Example:")
            .AppendLine(border)
            .AppendLine(string.Format("{0,20} | {1,20}", "first", "second"))
            .AppendLine(string.Format("{0,20} | {1,20}", first.ToString(), second.ToString()))
            .AppendLine(border)
            .AppendLine(string.Format("{0,20} | {1,20} | {2,20}", "added", "subtracted", "multiplied"))
            .AppendLine(string.Format("{0,20} | {1,20} | {2,20}", added.ToString(), subtracted.ToString(), multiplied.ToString()))
            .AppendLine(border)
            .AppendLine(string.Format("{0,20} | {1,20} | {2,20}", string.Join(" ", added.Coefficients), string.Join(" ", subtracted.Coefficients), string.Join(" ", multiplied.Coefficients)))
            .AppendLine(border);

            Console.WriteLine(print.ToString());

            // test with your input
            Console.Write("Try it yourself! \nEnter first polynomial coefficients as integer numbers separated by space: ");
            first = new Polynomial(ConvertStringOfIntsToArray(Console.ReadLine()));

            Console.Write("Enter second polynomial coefficients as integer numbers separated by space: ");
            second = new Polynomial(ConvertStringOfIntsToArray(Console.ReadLine()));

            added      = first + second;
            subtracted = first - second;
            multiplied = first * second;

            // print
            print.Clear()
            .AppendLine(border)
            .AppendLine(string.Format("{0,20} | {1,20}", "first", "second"))
            .AppendLine(string.Format("{0,20} | {1,20}", first.ToString(), second.ToString()))
            .AppendLine(border)
            .AppendLine(string.Format("{0,20} | {1,20} | {2,20}", "added", "subtracted", "multiplied"))
            .AppendLine(string.Format("{0,20} | {1,20} | {2,20}", added.ToString(), subtracted.ToString(), multiplied.ToString()))
            .AppendLine(border)
            .AppendLine(string.Format("{0,20} | {1,20} | {2,20}", string.Join(" ", added.Coefficients), string.Join(" ", subtracted.Coefficients), string.Join(" ", multiplied.Coefficients)))
            .AppendLine(border);

            Console.WriteLine(print.ToString());
        }