# Fibonacci Series Program in C#

Fibonacci Series Program in C#

##### What is the Fibonacci Series?

The Fibonacci series is nothing but a sequence of numbers in the following order:

The numbers in this series are going to start with 0 and 1. The next number is the sum of the previous two numbers. The formula for calculating the Fibonacci Series is as follows:

F(n) = F(n-1) + F(n-2) where:

F(n) is the term number.
F(n-1) is the previous term (n-1).
F(n-2) is the term before that (n-2).

##### What are the different ways to implement the Fibonacci in C#?

In C#, we can print the Fibonacci Series in two ways. They are as follows:

1. Iterative Approach
2. Recursion Approach
##### Iterative Approach to Print Fibonacci Series in C#:

This is the simplest approach and it will print the Fibonacci series by using the length. The following program shows how to use the iterative approach to print the Fibonacci Series in C#.

 public static void Fibonacci()         {             int num1 = 0, num2 = 1, num3, numberOfElements;             Console.Write("Enter the number of elements to Print : ");             numberOfElements = int.Parse(Console.ReadLine());             if (numberOfElements < 2)             {                 Console.Write("Please Enter a number greater than two");             }             else             {                 //First print first and second number                 Console.Write(num1 + " " + num2 + " ");                 //Starts the loop from 2 because 0 and 1 are already printed                 for (int i = 2; i < numberOfElements; i++)                 {                     num3 = num1 + num2;                     Console.Write(num3 + " ");                     num1 = num2;                     num2 = num3;                 }             }         }

Output

##### Recursive Approach to Print Fibonacci Series in C#:

In the Recursive Approach, we need to pass the length of the Fibonacci Series to the recursive method and then it will iterate continuously until it reaches the goal. Let us understand this with an example.

 static void Main(string[] args)         {               Console.Write("Please enter the Length of the Fibonacci Series : ");             int number = int.Parse(Console.ReadLine());             FibonacciSeries(0, 1, 1, number);             Console.ReadLine();         }            public static void FibonacciSeries(int firstNumber, int secondNumber, int counter, int number)         {                        Console.Write(firstNumber + " ");             if (counter < number)             {                 FibonacciSeries(secondNumber, firstNumber + secondNumber, counter + 1, number);             }         }

##### How to find the nth Fibonacci number in the Fibonacci Series in C#?

It is also possible to print the nth Fibonacci number from the Fibonacci series in C#. The following example prints the nth number from the Fibonacci series.

output

##### Without Using Recursive Function:

Let us understand how to implement this with an example. Here we are not going to use the Recursive function.

 static void Main(string[] args)         {             Console.Write("Please enter the Nth number of the Fibonacci Series : ");             int NthNumber = int.Parse(Console.ReadLine());             //Decrement the Nth Number by 1. This is because the series starts with 0             NthNumber = NthNumber - 1;             Console.Write(NthFibonacciNumber(NthNumber));             Console.ReadLine();         }         private static int NthFibonacciNumber(int number)         {             int firstNumber = 0, secondNumber = 1, nextNumber = 0;             // To return the first Fibonacci number              if (number == 0)                 return firstNumber;             for (int i = 2; i <= number; i++)             {                 nextNumber = firstNumber + secondNumber;                 firstNumber = secondNumber;                 secondNumber = nextNumber;             }             return secondNumber;         }

output

##### How to Print the Fibonacci Series up to a given number in C#?

Now we will see how to print the Fibonacci up to a given number in C#. Please have a look at the following program.

 private static void FibonacciNumber()         {             int firstNumber = 0, SecondNumber = 1, nextNumber, number;             Console.Write("Enter the number upto which print the Fibonacci series : ");             number = int.Parse(Console.ReadLine());             //First print first and second number             Console.Write(firstNumber + " " + SecondNumber + " ");             nextNumber = firstNumber + SecondNumber;             //Starts the loop from 2 because 0 and 1 are already printed             for (int i = 2; nextNumber < number; i++)             {                 Console.Write(nextNumber + " ");                 firstNumber = SecondNumber;                 SecondNumber = nextNumber;                 nextNumber = firstNumber + SecondNumber;             }         }

output