PolynomialsSum-and-Multiplication

using System;



class PolynomialsSumAndMultiplication
{
    static int lenghtofPolinomial = 0;
    static int[] polinomialCoef = new int[lenghtofPolinomial];
    static int[] result = new int [10];
    static int[] firstPolinomial = AddPolinomial();
    static int[] secondPolinomial = AddPolinomial();


    static int[] AddPolinomial()
    {
        Console.WriteLine("Enter lenght of polinomial:");
        lenghtofPolinomial = int.Parse(Console.ReadLine());
        polinomialCoef = new int[lenghtofPolinomial];

        for (int i = lenghtofPolinomial - 1; i >=0 ; i--)
        {
            Console.Write("x^{0} =", i);
            polinomialCoef[i] = int.Parse(Console.ReadLine());
        }
        return polinomialCoef;
    }
    static int[] PrintPolinomialsCoeficients(int[] polinomialCoef)
    {
        for (int i = polinomialCoef.Length - 1; i >=0 ; i--)
        {
            if (polinomialCoef[i] == 0)
            {
                continue;
            }
            if (i == 0)
            {
                Console.Write(polinomialCoef[i]);
            }
            else if (i == 1)
            {
                Console.Write("{0} * x", polinomialCoef[i]);
            }
            else
            {
                Console.Write("{0} * x^{1}", polinomialCoef[i], i);
            }
            if (i > 0)
            {
                Console.Write(" + ");
            }
        }
        Console.WriteLine("\n");

        return polinomialCoef;
    }
    static int[] SumPolinomials(int[] polinomialCoef)
    {
        int minLength = Math.Min(firstPolinomial.Length, secondPolinomial.Length);
        int maxLength = Math.Max(firstPolinomial.Length, secondPolinomial.Length);
        result = new int [maxLength];

        for (int i = maxLength - 1; i >=0 ; i--)
        {
            if (i < minLength)
            {
                result[i] = firstPolinomial[i] + secondPolinomial[i];
            }
            else if (i > firstPolinomial.Length - 1)
            {
                result[i] = secondPolinomial[i];
            }
            else if (i > secondPolinomial.Length - 1)
            {
                result[i] = firstPolinomial[i];
            }
        }

        return result;
    }
    static int[] SubtractionPolinomials(int[] polinomialCoef)
    {
        int minLength = Math.Min(firstPolinomial.Length, secondPolinomial.Length);
        int maxLength = Math.Max(firstPolinomial.Length, secondPolinomial.Length);
        result = new int[maxLength];

        for (int i = maxLength - 1; i >= 0 ; i--)
        {
            if (i < minLength)
            {
                result[i] = firstPolinomial[i] - secondPolinomial[i];
            }
            else if (i > firstPolinomial.Length - 1)
            {
                result[i] = - secondPolinomial[i];
            }
            else if (i > secondPolinomial.Length - 1)
            {
                result[i] = firstPolinomial[i];
            }
        }

        return result;
    }
    static int[] MultiplicationPolinomials(int[] polinomialCoef)
    {
        result = new int[firstPolinomial.Length + secondPolinomial.Length];

        for (int i = firstPolinomial.Length - 1; i >= 0; i--)
        {
            for (int j = secondPolinomial.Length - 1; j >= 0; j--)
            {
                result[i + j] = firstPolinomial[i] * secondPolinomial[j];

                if (result[i + j] == 0)
                {
                    continue;
                }
                if (i + j == 0)
                {
                    Console.Write(result[i + j]);
                }
                else if (i + j == 1)
                {
                    Console.Write("{0} * x", result[i + j]);
                }
                else
                {
                    Console.Write("{0} * x^{1} ", result[i + j], i + j);
                }
                if (i + j > 0)
                {
                    Console.Write(" + ");
                }
            }
        }
        Console.WriteLine();

        return result;
    }
    static void Main()
    {
        Console.WriteLine("\nFirst polinomial is:\n");
        PrintPolinomialsCoeficients(firstPolinomial);

        Console.WriteLine("\nSecond polinomial is:\n");
        PrintPolinomialsCoeficients(secondPolinomial);

        Console.WriteLine("\nSum of polinomials:\n");
        SumPolinomials(polinomialCoef);
        PrintPolinomialsCoeficients(result);

        Console.WriteLine("\nSubtraction of polinomials:\n");
        SubtractionPolinomials(polinomialCoef);
        PrintPolinomialsCoeficients(result);

        Console.WriteLine("\nMultiplication of polinomials:\n");
        MultiplicationPolinomials(polinomialCoef);

    }
}