using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        // 1.   Write a function that determines if a string starts with an upper-case letter A-Z

        PrintFirstLetterIsUppercase("arizona");

        PrintFirstLetterIsUppercase("Arizona");

        PrintFirstLetterIsUppercase("zebra");

        PrintFirstLetterIsUppercase("Zebra");

        PrintFirstLetterIsUppercase("1Zebra");

        // 2.   Write a function that determines the area of a circle given the radius

        Console.WriteLine("Circle area: {0} - radius = {1}:", CalculateRadius(107), 107);

        int radius = 107;

        Console.WriteLine("Circle area: {0} - radius = {1}:", Math.Round(Math.PI * radius * radius, 2), radius);

        // 3.   Add up all the values in an array

        Console.WriteLine("Sum: {0}:", SumArray(new int[] {1,2,3,4,5,6}));

        Console.WriteLine("Sum: {0}:", new int[] {1,2,3,4,5,6}.Sum());

    }

    private static void PrintFirstLetterIsUppercase(string word)

    {

        char[] wordChars = word.ToCharArray();

        int asciiCharacter = (int) wordChars[0];

        if (asciiCharacter >= 65 && asciiCharacter <= 91)

        {

            Console.WriteLine("{0} is uppercase", wordChars[0]);

        }

        else

        {

            Console.WriteLine("{0} is not uppercase", wordChars[0]);

        }

    }

    private static double CalculateRadius(int radius)

    {

        return Math.Round(Math.PI * (radius * radius), 2);

    }

​

    private static int SumArray(int[] numbers)

    {

        return numbers.Sum();

    }

}