An Array is an unordered sequence of elements. All the elements in an array have the same type, followed by a pair of square brackets, followed by the variable name.
   

int[] pinNumbers; //personal identification numbers

note: C and C++ programmers should note that the size of the array is not part of thedeclaration.

Arrays are reference type
The size of an array does not have to be a constant, it can be calculated at run time.

int size = int.Parse(Console.ReadLine());

    int[] pinNumbers = new int[size];

Its possible to create arrays of size 0. Useful in situations where the size is determined dynamically. Array with size 0 is not a null array.

Initializing Array Variable
i.e Initializing pinNumbers to an array of 4 int with the following values: 9,3,7,2

int[] pinNumber = new int[4] {9,3,7,2}; 
// the number in the curly bracket must match the size of the array

the value within the curly brace do not have to be constants.
   

Random r = new Random();

    int[] pinNumber = new int[4]{ r.next() %10, r.next() %10,
 r.next() %10, r.next() %10};

note: The system.Random class is a pseudo -random number generator. The Next method returns a nonnegative random number.

When initializing an array, you can omit the 'new' expression and the size of the array:

int[] pinNumbers {9,7,3,2};

   
Accessing Individual Array Elements

  To access an individual array element you must provide an index indicating which element you require.

int myNumber; 

    myNumber =  pinnumbers[3] ; 

you can also change the contents of an array by assigning a value to an indexed element:

myNumber = 167; 

pinnumbers[2] = myNumber; 

the initial element in an array is indexed 0 (zero) and not 1.

All array elements access is bounds-checked. when using an integer index that is less than 0 or greater than or equal to the lengh of the array, the compiler throws an indexOutOfRangeException

try 

    { 

        int[] pinnumbers ={9,3,7,2}; 

         Console.WritLine(pinNumber[4]); //error, the 4th element is at index 3 

   } 

   catch(indexOutOfRangeException ex) 

   { 

      ... 

   }