Firstly, use the DirectoryInfo object −//creating a DirectoryInfo object DirectoryInfo mydir = new DirectoryInfo(@"d:\amit");Now, use the GetFiles() method to get all the files −FileInfo [] f = mydir.GetFiles();To get the list of files in a directory, try to run the following code −Exampleusing System; using System.IO; namespace Demo {    class Program {       static void Main(string[] args) {          //creating a DirectoryInfo object          DirectoryInfo mydir = new DirectoryInfo(@"d:\amit");          // getting the files in the directory, their names and size          FileInfo [] f = mydir.GetFiles();          foreach (FileInfo file in f) {             Console.WriteLine("File Name: {0} Size: {1}", file.Name, file.Length);          }          Console.ReadKey();       }    } }

To concatenate two lists, use AddRange() method.Set the first list −var products1 = new List < string > (); products1.Add("Belts"); products1.Add("Tshirt"); products1.Add("Trousers");Set the second list −var products2 = new List < string > (); products2.Add("Footwear"); products2.Add("Electronics");To concatenate both the lists −products1.AddRange(products2);The following is the complete code −Example Live Demousing System.Collections.Generic; using System; namespace Demo {    public static class Program {       public static void Main() {          var products1 = new List < string > ();          products1.Add("Belts");          products1.Add("Tshirt");          products1.Add("Trousers");     ... Read More

Firstly, add elements −IDictionary d = new Dictionary(); d.Add(1,97); d.Add(2,89); d.Add(3,77); d.Add(4,88);Now, get the keys −List myList = new List(d.Keys);To iterate −foreach (int k in myList) {    Console.WriteLine("{0}, {1}", k, d[k]); }The following is an example −Example Live Demousing System; using System.Collections.Generic; public class Demo {    public static void Main() {       IDictionary < int, int > d = new Dictionary < int, int > ();       d.Add(1, 97);       d.Add(2, 89);       d.Add(3, 77);       d.Add(4, 88);       List < int > myList = new List < int > (d.Keys);           foreach(int k in myList) {          Console.WriteLine("{0}, {1}", k, d[k]);       }    } }Output1, 97 2, 89 3, 77 4, 88

To iterate efficiently through an array of integers of unknown size in C# is easy. Let’s see how.Firstly, set an array, but do not set the size −int[] arr = new int[] { 5, 7, 2, 4, 1 };Now, get the length and iterate through an array using for loop −for (int i = 0; i< arr.Length; i++) {    Console.WriteLine(arr[i]); }Let us see the complete example −Example Live Demousing System; public class Program {    public static void Main() {       int[] arr = new int[] {          5,          7,          2,          4,          1       };       // Length       Console.WriteLine("Length:" + arr.Length);       for (int i = 0; i < arr.Length; i++) {          Console.WriteLine(arr[i]);       }    } }OutputLength:5 5 7 2 4 1

C# has no built-in Math type. For the same, use a Dictionary.Firstly, create a Dictionary −Dictionary d = new Dictionary(); d.Add("keyboard", 1); d.Add("mouse", 2);Get the keys −var val = d.Keys.ToList();Now, use the foreach loop to iterate over the Map −foreach (var key in val) {    Console.WriteLine(key); }To iterate it, try to run the following code −Example Live Demousing System; using System.Collections.Generic; using System.Linq; class Program {    static void Main() {       Dictionary d = new Dictionary();       d.Add("keyboard", 1);       d.Add("mouse", 2);       // get keys   ... Read More

Use the new operator to instantiate a class in C#.Let’s say our class is Line. Instantiation will create a new object as shown below −Line line = new Line();Using the object, you can now call the method −line.setLength(6.0);Let us see the example −Example Live Demousing System; namespace LineApplication {    class Line {       private double length; // Length of a line       public Line() {          Console.WriteLine("Object is being created");       }       public void setLength( double len ) {          length = len; ... Read More

To insert an item in an already created ArrayList, use the Insert() method.Firstly, set elements −ArrayList arr = new ArrayList(); arr.Add(45); arr.Add(78); arr.Add(33);Now, let’s say you need to insert an item at 2nd position. For that, use the Insert() method −// inserting element at 2nd position arr.Insert(1, 90);Let us see the complete example −Example Live Demousing System; using System.Collections; namespace Demo {    public class Program {       public static void Main(string[] args) {          ArrayList arr = new ArrayList();          arr.Add(45);          arr.Add(78);       ... Read More

Use a while loop to input multiple values from the user in one line.Let’s say you need to get the elements of a matrix. Get it using Console.ReadLine() as shown below −Console.Write("Enter elements - Matrix 1 : "); for (i = 0; i < m; i++) {    for (j = 0; j < n; j++) {       arr1[i, j] = Convert.ToInt16(Console.ReadLine());    } }The following is an example showing how we can input multiple values from user −Example Live Demousing System; namespace Demo {    public class Program {       public static void Main(string[] args) ... Read More

To initialize a list to an empty list in C#, set it like the following statement without any elements −List list = new List();Now, use the Any() method to check whether the list is empty or not −bool chk = !list.Any();Let us see the complete code −Example Live Demousing System; using System.Collections.Generic; using System.Linq; public class Program {    public static void Main() {       // empty list       List list = new List();       // check for empty list       bool chk = !list.Any();       if(chk) {          Console.WriteLine("List is Empty!");       } else {          Console.WriteLine("List isn't Empty!");       }    } }OutputList is Empty!

To initialize a dictionary to an empty dictionary, use the Clear() method. It clears the dictionary and forms it as empty.dict.Clear();After that, use the Dictionary count property to check whether the list is empty or not −if (dict.Count == 0) {    Console.WriteLine("Dictionary is empty!"); }Let us see the complete code −Example Live Demousing System; using System.Collections.Generic; using System.Linq; namespace Demo {    public class Program {       public static void Main(string[] args) {          var dict = new Dictionary < string, string > ();          dict.Clear();          if (dict.Count == 0) {             Console.WriteLine("Dictionary is empty!");          }       }    } }OutputDictionary is empty!