how to declare array and string in c#?

Answer 1

string[] myStrArray = new string[3];

Will create a new string array with 3 elements.

Answer 2

Declaring an Array:
int[] myIntArray = new int[5] { 1, 2, 3, 4, 5 };
//the above declares an array of 5 integers

Declaring a string
string MyString = "Here goes my string.";

Answer 3

Declare a C# array with the following syntax:
type[] array-name;

For example:
int[] myIntArray

Declare a C# String with the following syntax:
type[] String-name;
string myString;

You can even use in this way
string myString = "Hi there";