Collections

 The concept of “collections” is basically developed from “Arrays”.
 Already you know that, arrays are multiple value containers of fixed type.
 In order to hold different types of values on the same array, you require collections.
 Another advantage of collections is those are dynamic sizable. In other words, the array is of fixed size and the collection is of dynamic size.
 Finally, if you don’t know how many values are to be stored in the array at the time of its declaration, you require to use “collections”; (or) if you want to store different type of values in the same array, at that case also, you require to use “collections”.
 .NET offers some pre-defined classes for maintenance of collections.
Collection Classes:

 List:
1) Contains n no. of values of same type. It’s a generic class.
2) This is member of “System.Collections.Generic” namespace.
 ArrayList:
1) Contains n no. of values of different types.
2) This is member of “System.Collections” namespace.
Implementation of “List” class:

 Import namespace:
using System.Collections.Generic;
 Create instance:
List<data type> obj = new List<data type>();
 Add values:
obj.Add(value);
 Get the currently existing no. of values in the collection:
obj.Count;
 Get the individual element in the collection:
obj[index];
Implementation of “ArrayList” class:
 Import namespace:
using System.Collections;
 Create instance:
ArrayList obj = new ArayList();
 Add values:
obj.Add(value);
 Get the currently existing no. of values in the collection:
obj.Count;
 Get the individual element in the collection:
obj[index];

“List” Class

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

namespace ListClass
{
class Program
{
static void Main(string[] args)
{
List<string> MyMessages = new List<string>();
MyMessages.Add("Good Morning");
MyMessages.Add("Good Afternoon");
MyMessages.Add("Good Evening");
MyMessages.Add("Good Night");
//MyMessages.Add(10); //error
Console.WriteLine(MyMessages.Count + " messages found.\n");
foreach (string s in MyMessages)
{
Console.WriteLine(s);
}
Console.Read();
}
}
}
COllections

“ArrayList” Class

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

namespace ArrayListClass
{
class Program
{
static void Main(string[] args)
{
ArrayList al = new ArrayList();
al.Add("Hai");
al.Add("How r u");
al.Add(1000);
al.Add(true);
al.Add(DateTime.Now);
Console.WriteLine(al.Count + " values found.\n");
for (int i = 0; i < al.Count; i++)
Console.WriteLine(al[i]);
Console.Read();
}
}
}
COllections