Fibonacci Series in C#

The Fibonacci series is a sequence of numbers where each number is the sum of the two preceding numbers. The series typically starts with 0 and 1, producing the sequence: 0, 1, 1, 2, 3, 5, 8, 13, 21, and so on.

In C#, there are multiple ways to generate the Fibonacci series, including iterative and recursive approaches.

Using Iterative Approach

The iterative approach uses a loop to calculate each Fibonacci number by adding the two previous numbers −

using System;

public class FibonacciIterative {
   public static void Main(string[] args) {
      int val1 = 0, val2 = 1, val3, i, n;
      n = 8;
      Console.WriteLine("Fibonacci series using iterative approach:");
      Console.Write(val1 + " " + val2 + " ");
      
      for(i = 2; i < n; i++) {
         val3 = val1 + val2;
         Console.Write(val3 + " ");
         val1 = val2;
         val2 = val3;
      }
   }
}

The output of the above code is −

Fibonacci series using iterative approach:
0 1 1 2 3 5 8 13

Using Recursive Approach

The recursive approach defines a function that calls itself to calculate Fibonacci numbers −

using System;

public class FibonacciRecursive {
   public static int Fibonacci(int n) {
      if(n <= 1) {
         return n;
      }
      return Fibonacci(n - 1) + Fibonacci(n - 2);
   }
   
   public static void Main(string[] args) {
      int n = 8;
      Console.WriteLine("Fibonacci series using recursive approach:");
      
      for(int i = 0; i < n; i++) {
         Console.Write(Fibonacci(i) + " ");
      }
   }
}

The output of the above code is −

Fibonacci series using recursive approach:
0 1 1 2 3 5 8 13

Using Array to Store Fibonacci Numbers

You can also store the Fibonacci series in an array for later use −

using System;

public class FibonacciArray {
   public static void Main(string[] args) {
      int n = 10;
      int[] fibonacci = new int[n];
      
      if(n >= 1) fibonacci[0] = 0;
      if(n >= 2) fibonacci[1] = 1;
      
      for(int i = 2; i < n; i++) {
         fibonacci[i] = fibonacci[i - 1] + fibonacci[i - 2];
      }
      
      Console.WriteLine("Fibonacci series stored in array:");
      for(int i = 0; i < n; i++) {
         Console.Write(fibonacci[i] + " ");
      }
   }
}

The output of the above code is −

Fibonacci series stored in array:
0 1 1 2 3 5 8 13 21 34

Comparison of Approaches

Conclusion

The Fibonacci series can be generated in C# using iterative, recursive, or array-based approaches. The iterative method is most efficient for larger sequences, while the recursive approach is simpler to understand but less efficient for large numbers due to repeated calculations.