using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Linq;

public class MainClass{
   public static void Main(){
       int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
       var query = numbers.First();
       Console.WriteLine("The first element in the sequence");
       Console.Write(query);
       query = numbers.Last();
       Console.WriteLine("The last element in the sequence");
       Console.Write(query);
       Console.WriteLine("The first even element in the sequence");
       query = numbers.First(n => n % 2 == 0);
       Console.Write(query);
       Console.WriteLine("The last even element in the sequence");
       query = numbers.Last(n => n % 2 == 0);
       Console.Write(query);
   }
}

    

   
 
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Reflection;
using System.Linq;
using System.Xml;
using System.Xml.Linq;
public static class Extensions {
    public static string SpaceToUnderscore(this string source) {
        char[] cArray = source.ToCharArray();
        string result = null;

        foreach (char c in cArray) {
            if (Char.IsWhiteSpace(c))
                result += "_";
            else
                result += c;
        }

        return result;
    }
}
class Program {
    static void Main(string[] args) {
        string s = "This is a test";
        Console.WriteLine(s.SpaceToUnderscore());
    }
}

    

using System;

static class MainClass {
public static int ConvertToBase(this int i, int baseToConvertTo) {
if (baseToConvertTo < 2 || baseToConvertTo > 10)
throw new ArgumentException(“Value cannot be converted to base ” + baseToConvertTo.ToString());
int result = 0;
int iterations = 0;
do {
int nextDigit = i % baseToConvertTo;
result += nextDigit * (int)Math.Pow(10, iterations);
iterations++;
i /= baseToConvertTo;
}
while (i != 0);
return result;
}
static void Main() {
try {
int x = 591;
for (int i = 2; i <= 10; i++) { Console.WriteLine("{0} in base {1} is {2}", x, i, x.ConvertToBase(i)); } } catch (Exception ex) { Console.WriteLine("Exception: {0}", ex.Message); } } } [/csharp]

   
 

using System;
using System.Collections.Generic;
using System.Linq;
public class MainClass {
    public static void Main() {
        string[] names = { "J", "P", "G", "Pa" };

        IEnumerable<string> filtered = Enumerable.Where(names,n => n.Contains("a"));
        IEnumerable<string> sorted = Enumerable.OrderBy(filtered, n => n.Length);
        IEnumerable<string> finalQuery = Enumerable.Select(sorted,n => n.ToUpper());

    }
}

    

   
 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
    public static void Main() {
        var wordsA = new string[] { "c", "ap", "b" };
        var wordsB = new string[] { "c", "ap", "b" };

        bool match = wordsA.Equals(wordsB);

        Console.WriteLine("The sequences match: {0}", match);
    }
}

    

   
 
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Linq;

public class MainClass{
   public static void Main(){
            int[] numbers = {1, 2, 3, 4};
            int[] numbers2 = {1, 1, 3, 3};
            Console.Write(numbers.Except(numbers2));
   }
}

    

   
 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
    public static void Main() {
        int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };
        int[] numbersB = { 1, 3, 5, 7, 8 };

        IEnumerable<int> aOnlyNumbers = numbersA.Except(numbersB);

        Console.WriteLine("Numbers in first array but not second array:");
        foreach (var n in aOnlyNumbers) {
            Console.WriteLine(n);
        }
    }
}