C#

ADO.NET.cs

public void ReadDataFromDatabaseUsingDA()
{
    // 1
    // Open connection
    using (SqlConnection c = new SqlConnection(@"Data Source=PCName\\SQLEXPRESS;Initial Catalog= DBEmployeeDetailsMock;Integrated Security=True"))
    {
        c.Open();
        // 2
        // Create new DataAdapter
        using (SqlDataAdapter a = new SqlDataAdapter("SELECT * FROM EmployeeIDs", c))
        {
            // 3
            // Use DataAdapter to fill DataTable
            DataTable t = new DataTable();
            a.Fill(t);
        }
        
    }
    foreach (DataRow dr in t.Rows)
    {
        Console.WriteLine(dr["Employee_Id"].ToString());
        Console.WriteLine(dr["Employee_Name"].ToString());
        Console.WriteLine(Convert.ToDateTime(dr["DateOfJoining"]).ToShortDateString());
        Console.WriteLine(dr["Email_Id"].ToString());
    }
}

public void ReadDataFromDatabaseUsingDR()
{
  using (SqlConnection connection = new SqlConnection(connectionString))
  using (SqlCommand command = new SqlCommand("select * from Requests where Complete = 0", connection))
  {
      connection.Open();  
      using (SqlDataReader reader = command.ExecuteReader())
      {
          while (reader.Read())
          {
              Console.WriteLine(reader["Username"].ToString());
              Console.WriteLine(reader["Item"].ToString());
              Console.WriteLine(reader["Amount"].ToString());
              Console.WriteLine(reader["Complete"].ToString());
          }
      }
   }
}

public void InsertToDatabase()
{
    SqlConnection sqlConnectionString = new SqlConnection
    (@"Data Source=PCName\\SQLEXPRESS;Initial Catalog= DBEmployeeDetailsMock;Integrated Security=True");
    
    //In case of update
    //command.Text = "UPDATE Student SET Address = @add, City = @city Where FirstName = @fn and LastName = @add";
    SqlCommand command = new SqlCommand("Insert into Employees values (@Employee_Id,@Employee_Name,@DateOfJoining,@Email_Id)", sqlConnectionString);
    command.Parameters.Add(new SqlParameter("@Employee_Id", "001"));
    command.Parameters.Add(new SqlParameter("@Employee_Name", "John"));
    command.Parameters.Add(new SqlParameter("@DateOfJoining", Convert.ToDateTime("03/20/2012")));
    command.Parameters.Add(new SqlParameter("@Email_Id", "John@yahoo.com"));

    sqlConnectionString.Open();
    command.ExecuteNonQuery();
    sqlConnectionString.Close();  
}

EmployeeValidator.cs

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Data;
using System.Collections;
using System.Xml;
using System.Xml.Linq;
using System.Text.RegularExpressions;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.Sql;
using System.Xml.Serialization;


namespace EmployeeValidation
{
    public class EmployeeValidator
    {
        /*
        * Do not remove the attached TestProject. It is meant for auto evaluation of your source code.
        * Do not attach any test classess to the attached test project.
        * Do not attach any new test projects.
        * You are not required to write any automated test cases. You are supposed to write only the code.
        */

        public void ProcessData(string xmlFilePath, string xmlFileName, SqlConnection connection)
        {
			//Do your logic here
			EmployeeValidator empVal = new EmployeeValidator();
			List<Employee> lstEmp = new List<Employee>();

			//Step 1           
			//ReadAllEmployeesFromXmlFile
			lstEmp = empVal.ReadAllEmployeesFromXmlFile(xmlFilePath, xmlFileName);

			//Step 2           
			//PickValidEmployees
			lstEmp = empVal.PickValidEmployees(lstEmp);

			//Step 3
			//SaveValidEmployeesToDataBase
			empVal.SaveValidEmployeesToDB(lstEmp, connection);

        }

        public List<Employee> ReadAllEmployeesFromXmlFile(string xmlFilePath, string xmlFileName)
        {
			//Read the employee details from the xml file and return it in List collection
			//Do not hardcode the filename and the file path here
			List<Employee> Emplst = new List<Employee>();
			XElement xelement = XElement.Load(xmlFilePath + xmlFileName);
			IEnumerable<XElement> allEmployees = xelement.Elements();

			foreach (var employee in allEmployees)
			{
				Emplst.Add(new Employee()
				{
					EmployeeId = employee.Element("EmployeeId").Value,
					EmployeeName = employee.Element("EmployeeName").Value,
					EmailId = employee.Element("EmailId").Value,
					DateOfJoining = employee.Element("DateOfJoining").Value
				});
			}

			return Emplst;

            //Do not return the date with time appended to it.
        }

        public List<Employee> PickValidEmployees(List<Employee> employees)
        {
			//Pick the valid employees from the List collection
			//Return the valid employees in a List
			List<Employee> empList = new List<Employee>();
			Regex IsNumeric = new Regex(@"\d+");
			Regex IsAlphaNumeric = new Regex(@"^\d*[a-zA-Z]+");
			Regex IsValidEmail = new Regex(@"^(?("")(""[^""]+?""@)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])@))(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9]{2,17}))$");

			empList = employees.Select(x => employees.Find(
				m => m.EmployeeName != null &&
				m.EmployeeName != string.Empty &&
				IsNumeric.IsMatch(m.EmployeeId.ToString()) &&
				IsAlphaNumeric.IsMatch(m.EmployeeName)
				)).Distinct().ToList();
            
            return empList;//Return only valid employees in List
        }

        public void SaveValidEmployeesToDB(List<Employee> employees, SqlConnection connection)
        {
			//Do not Prefix Database name in the SQL Query. Query should be "Insert into SBA.TableName"
			//Should not be "Insert into DatabaseName.SBA.TableName"
			//Do not hardcode the connection string here
			string query = @"Insert into SBA.Employees(EmployeeId,EmployeeName,EmailId,DateOfJoining)
							values(@EmployeeId,@EmployeeName,@EmailId,@DateOfJoining)";

			connection.Open();
			using (SqlCommand cmd = new SqlCommand(query, connection))
			{
				foreach (var employee in employees)
				{
					cmd.Parameters.AddWithValue("@EmployeeId", employee.EmployeeId);
					cmd.Parameters.AddWithValue("@EmployeeName", employee.EmployeeName);
					cmd.Parameters.AddWithValue("@EmailId", employee.EmailId);
					cmd.Parameters.AddWithValue("@DateOfJoining", employee.DateOfJoining);
					int i = cmd.ExecuteNonQuery();
				}
			}
			connection.Close();
        }
    }
}

FileSystemWatcher.cs

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

namespace FileSystemDemo
{
  public class Watcher
    {
        static void Main(string[] args)
        {
            FileSystemWatcher watcher = new FileSystemWatcher();
                      
            //Replace the path to your local path
            string _path = @"C:\Users\153239\Desktop\FileSystemTest\";

            watcher.Path = _path;
            watcher.EnableRaisingEvents = true;
            watcher.Created += new FileSystemEventHandler(OnChanged);
            watcher.Deleted += new FileSystemEventHandler(OnChanged);
            watcher.Changed += new FileSystemEventHandler(OnChanged);

            Console.WriteLine("FileSystemWatcher is listening to changes in the path :\n\n" + _path);
            Console.Read();

        }
        // Define the event handlers. 
        private static void OnChanged(object source, FileSystemEventArgs e)
        {
            // Specify what is done when a file is changed, created, or deleted.
            Console.WriteLine("File: " + e.FullPath + " " + e.ChangeType);
        }
    }
}

Important.cs

string s = "Please ask for on arrival";

//Reverse string character wise
var s_char = s.ToCharArray();
Array.Reverse(s_char);
Console.WriteLine(new String(s_char));

//Write to a file
FileStream fs = new FileStream("test.txt", FileMode.Append, FileAccess.Write);
StreamWriter sw = new StreamWriter(fs);
sw.WriteLine("Entering this string into the text file.");
sw.Flush();
sw.Close();
fs.Close();

//Read character by character from a file
char ch;
StreamReader sr = new StreamReader("test.txt");
do{
  ch = (char)reader.Read();
  Console.WriteLine(ch)
}while(!reader.EndofStream);
reader.Close();
reader.Dispose();

//Reverse words in a string
var s_split = s.Split(' ');
Array.Reverse(s_split);
Console.WriteLine(string.Join(" ", s_split));

//Search a substring and print
string search = "ask";
var askIndex = s.IndexOf("ask");
Console.WriteLine(s.Substring(askIndex, search.Length));

//Insert a substring before a given word
string name = "Akshay ";
Console.WriteLine(s.Insert(s.IndexOf("on"), name));

//Replace a substring
Console.WriteLine(s.Replace("Please a", "A"));

//REGULAR EXPRESSIONS YOU SHOULD KNOW:
Matching a Username: /^[a-z0-9_-]{3,16}$/
Matching a Password: /^[a-z0-9_-]{6,18}$/
Matching a Hex Value: /^#?([a-f0-9]{6}|[a-f0-9]{3})$/
Matching a Slug: /^[a-z0-9-]+$/
Matching an Email: /^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/
Matching a URL: /^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$/
Matching an IP Address: /^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/
Matching an HTML Tag: /^<([a-z]+)([^<]+)*(?:>(.*)<\/\1>|\s+\/>)$/
  
//Using Regex.Match
Match m = Regex.Match("123 Axxxxy", @"A.*y");
if (m.Success)
{
    Console.WriteLine("Value  = " + m.Value);
    Console.WriteLine("Length = " + m.Length);
    Console.WriteLine("Index  = " + m.Index);
}

LINQ Queries.cs

////LINQ Queries////

//--LINQ to Objects--//
//Finding repeated values in a list
this.numberList.GroupBy(num => num).Where(grp => grp.Count() > 1).Select(grp => grp.Key);

//Output Elements in Ascending order
var dispFruits = from fruits in this.fruitNameList orderby fruits ascending select fruits;
var dispFruits = this.fruitNameList.OrderBy(f => f.Length).Select(f => f);

//GroupBy
var numberGroups = 
            from n in numbers 
            group n by n % 5 into g 
            select new { Remainder = g.Key, Numbers = g };

//Using where clause
var expensiveInStockProducts = 
    from p in products 
    where p.UnitsInStock > 0 && p.UnitPrice > 3.00M 
    select p
    
//Getting elements having length shorter their index in an array
var shortDigits = digits.Where((digit, index) => digit.Length < index); 

//First or Default with condition
Product product789 = products.FirstOrDefault(p => p.ProductID == 789);

//Get Second number in the list greater than 5
int fourthLowNum = ( 
        from n in numbers 
        where n > 5 
        select n) 
        .ElementAt(1);

//--LINQ to SQL--//
//Reading from Database
static void Main(string[] args)
{
    MyDatabase db = new MyDatabase();
     var salesDept = from e in db.Employees
                    where e.Department == "Sales"
                    select e;

    foreach (var employee in salesDept)
        Console.WriteLine(employee.ID + " " + employee.Name);
    Console.ReadLine();
}

//Writing to Database
static void Main(string[] args)
{
    MyDatabase db = new MyDatabase();

    db.ExecuteCommand("CREATE TABLE Employees (ID int, Name varchar(50), Department varchar(50))");

    Employee employee1 = new Employee();
    employee1.ID = 101;
    employee1.Name = "John Smith";
    employee1.Department = "Sales";
    db.Employees.InsertOnSubmit(employee1);
    db.SubmitChanges();
}

//--LINQ to XML--//
//To Fetch Values under Root Element
static void Main(string[] args)
{
    XElement xelement = XElement.Load(@"C:\Employees.xml");
    IEnumerable<XElement> employees = xelement.Elements();
    Console.WriteLine("List of all Employee Names :");
    foreach (var employee in employees)
    {
        Console.WriteLine(employee.Element("Name").Value);
    }
    Console.ReadKey();
}

//To Fetch using attributes of the elements
static void Main(string[] args)
{
    XElement xelement = XElement.Load("C:\\Employees.xml");
    var homePhone = from phoneno in xelement.Elements("Employee")
                    where (string)phoneno.Element("Phone").Attribute("Type") == "Home"
                    select phoneno;
    Console.WriteLine("List HomePhone Nos.");
    foreach (XElement xEle in homePhone)
    {
        Console.WriteLine(xEle.Element("Phone").Value);
    }
    Console.ReadKey();
}

ReadWriteFromFile.cs

////READ FROM A FILE////
// Example #1
// Read the file as one string.
string text = System.IO.File.ReadAllText(@"C:\Users\Public\TestFolder\WriteText.txt");

// Display the file contents to the console. Variable text is a string.
System.Console.WriteLine("Contents of WriteText.txt = {0}", text);

// Example #2
// Read each line of the file into a string array. Each element
// of the array is one line of the file.
string[] lines = System.IO.File.ReadAllLines(@"C:\Users\Public\TestFolder\WriteLines2.txt");

// Display the file contents by using a foreach loop.
System.Console.WriteLine("Contents of WriteLines2.txt = ");
foreach (string line in lines)
{
    // Use a tab to indent each line of the file.
    Console.WriteLine("\t" + line);
}


////WRITE TO A FILE////
// Example #1: Write an array of strings to a file.
// Create a string array that consists of three lines.
string[] lines = { "First line", "Second line", "Third line" };
// WriteAllLines creates a file, writes a collection of strings to the file,
// and then closes the file.  You do NOT need to call Flush() or Close().
System.IO.File.WriteAllLines(@"C:\Users\Public\TestFolder\WriteLines.txt", lines);


// Example #2: Write one string to a text file.
string text = "A class is the most powerful data type in C#. Like a structure, " +
               "a class defines the data and behavior of the data type. ";
// WriteAllText creates a file, writes the specified string to the file,
// and then closes the file.    You do NOT need to call Flush() or Close().
System.IO.File.WriteAllText(@"C:\Users\Public\TestFolder\WriteText.txt", text);

// Example #3: Write only some strings in an array to a file.
// The using statement automatically flushes AND CLOSES the stream and calls 
// IDisposable.Dispose on the stream object.
// NOTE: do not use FileStream for text files because it writes bytes, but StreamWriter
// encodes the output as text.
using (System.IO.StreamWriter file = 
    new System.IO.StreamWriter(@"C:\Users\Public\TestFolder\WriteLines2.txt"))
{
    foreach (string line in lines)
    {
        // If the line doesn't contain the word 'Second', write the line to the file.
        if (!line.Contains("Second"))
        {
            file.WriteLine(line);
        }
    }
}

// Example #4: Append new text to an existing file.
// The using statement automatically flushes AND CLOSES the stream and calls 
// IDisposable.Dispose on the stream object.
using (System.IO.StreamWriter file = 
    new System.IO.StreamWriter(@"C:\Users\Public\TestFolder\WriteLines2.txt", true))
{
    file.WriteLine("Fourth line");
}

SerializerDeserializer.cs

////To serialize Vehicle class object to xml file.////
public static void SerializeToXml(Vehicle vehicle)
{
    XmlSerializer xmlSerilizer = new XmlSerializer(typeof(Vehicle));
    TextWriter textWriter = new StreamWriter(@"C:\vehicle.xml");
    xmlSerilizer.Serialize(textWriter, vehicle);// Only public member are serialzed.
    textWriter.Close();
    Console.WriteLine("\n Vehicle class object has been serialized !");
}


////Binary Serialization and Deserialization////
//This method serialize the object of account class.
public void SerializeAccObj(BinaryFormatter bFormatter, FileStream fStream, Account accObj)
{
    fStream = new FileStream(@"C:\BinarySerializeDemo.bin", FileMode.Create);
    bFormatter.Serialize(fStream, accObj);
    fStream.Close();

    Console.WriteLine("\nData is Serialized Successfully with Binary Formatter.");
}
//This method deserialize the object of account class.
public void DeserializeAccObj(BinaryFormatter bFormatter, FileStream fStream, Account accObj)
{
    fStream = new FileStream(@"C:\BinarySerializeDemo.bin", FileMode.Open);
    accObj = bFormatter.Deserialize(fStream) as Account;
    fStream.Close();
    Console.WriteLine("\n------Restoring the object back to its former state------");
}

Globalization:
http://msdn.microsoft.com/en-us/library/System.Globalization.aspx
http://msdn.microsoft.com/en-us/library/system.globalization.cultureinfo(v=vs.80).aspx