CalcTriangleSurface

using System;

class CalcTriangleSurface
{
    static void Main()
    {
        Console.WriteLine("Calculate the surface of a triangle! Select how : by given ");
        Console.WriteLine("1-side and an altitude to it");
        Console.WriteLine("2-three sides");
        Console.WriteLine("3-two sides and an angle between them ?");
        sbyte select = sbyte.Parse(Console.ReadLine());
        if (select == 1)
        {
            Console.WriteLine("Enter side value ");
            double side = double.Parse(Console.ReadLine());
            Console.WriteLine("The Altitude to this side is ");
            double altitude = double.Parse(Console.ReadLine());
            Console.WriteLine("The surface is: {0} ", ByGivenSideAndAltitude(side, altitude));
        }
        if (select == 2)
        {
            Console.WriteLine("Enter side a = ");
            double sideA = double.Parse(Console.ReadLine());
            Console.WriteLine("Enter side b = ");
            double sideB = double.Parse(Console.ReadLine());
            Console.WriteLine("Enter side c = ");
            double sideC = double.Parse(Console.ReadLine());
            Console.WriteLine("The surface is: {0} ", ByGivenSides(sideA, sideB, sideC));
        }
        if (select == 3)
        {
            Console.WriteLine("Enter side a = ");
            double sideA = double.Parse(Console.ReadLine());
            Console.WriteLine("Enter side b = ");
            double sideB = double.Parse(Console.ReadLine());
            Console.WriteLine("Enter angle (in degrees)");
            double angle = double.Parse(Console.ReadLine());
            Console.WriteLine("The surface is: {0} ", UseSineCosine(sideA, sideB, angle));
        }
        if (select >= 4 )
        {
            Console.WriteLine("Your choice is not correct");
        }
    }
    static double ByGivenSideAndAltitude(double side, double altitude)
    {
        return side * altitude / 2D;
    }
    static double ByGivenSides(double sideA, double sideB, double sideC)
    {
        double i = (sideA + sideB + sideC) / 2D;
        return Math.Round(Math.Sqrt(i * (i - sideA) * (i - sideB) * (i - sideC)), 1);
    }
    static double UseSineCosine(double sideA, double sideB, double degrees)
    {
        double angle = Math.PI * degrees / 180.0;
        return (sideA * sideB * Math.Sin(angle)) / 2D;
    }
}