Before Solving Fibonacci Series you need to know what is Fibonacci Series.

**Fibonacci Series** is a numerical sequence, in which first two number is equal and each remaining number is equal to the previous two number.

Example :-

1 1 2 3 5 8 13 21 34 ......

**Now moving to your question **
as i getting your question you are looking for a Fibonacci series for array with 3 element.

**Solution**
using System;
using System.Collections.Generic;
using System.Text;
namespace Fibonacci_Series
{
class Program
{
static void Main(string[] args)
{
int[] arr1 = { 1, 2, 100 };
int n1, n2;
n1 = n2 = arr1[0]; Console.WriteLine(n1);
while (n2 < arr1[2])
{
Console.WriteLine(n2);
n2 += n1; n1 = n2 - n1;
}
Console.ReadLine();
}
}
}

BTW: "Please" has a total of two "e"s. Sentences start with a capital letter. Punctuation is used to separate sentences. Sentences contain at least a single subject and predicate. This should have been explained to you early in your school life. Ignoring all this makes you look like a whining child.