Collection

1.What is an Array ? What are different ways of writing an Array ?
Array is a datastructure that stores a collection of value that are of same data type.
diff ways of writing an array are-
a)specify the data length in declaration.
int [] count= new int[5];

b) int[] count = new int[] { 1, 2, 3 };
skip the length but have to specify the value.

c)int[] count = new int[2] { 1, 2, 3 };
both a and b. one thing should be taken care here the length of int array should be equal
to number of values specified.

2.Array is reference type or value type ?
Reference Type 

3.How do you search an item in an Array ?

The BinarySearch static method of Array class can be used to search for an item in a array. . The method takes at least two parameters - an array and an object (the item you are looking for). If an item found in an array, the method returns the index of the item (based on first item as 0^th item),  else method returns a negative value.

eg- 
 string[] name = new string[] { "chai", "alex", "dave" };         

int i=Array.BinarySearch(name, "dfsdf");  

i returns a negative value.
 

4.How to achieve Deep copy and Shallow copy using Array ?
Deep Copy-- By using Array.CopyTo
Shallow Copy---Array.Clone()

5.What are different types of an Array ?
a) Single dimensional Array
b) Multidimensional Array
c) Jaggd Array

6.Can diff data types be stored in a single Array?
No

7.Where does array index starts ?
Array index starts at Zero.
Suppose you have int [] count= {1,2,3} then
int[0] will give you "1".

8.Give an example of accessing Array using foreach loop.
 string[] name = new string[] { "chai", "alex", "dave" };           
 foreach (string a in name)
{
      Console.WriteLine(a.ToString());               
}

9. How do you sort an item in Array in reverse order ?
Use Count and Reverse property of an array.
eg-
int[] count = new int[] { 1, 2, 3,6,8,4 };
 Array.Sort(count);
 Array.Reverse(count);

10.Find the maximum no in an array.
you can use the property of array called Max or use the below algo-

11.Convert arraylist to string array 

Suppose you have a arraylist say with 3 string values- a[0]-name,a[1]-age,a[2]-gender.After converting using below code it will look like

string.Join(",",(string[])a.ToArray(typeof(string)))

string a=name,age,gender