Write a C program to print Fibonacci Series using recursion. Given an input number, we have to write a code to print Fibonacci series up to that number using Recursion.

This question is very important in terms of technical interviews.

You can check my previous post for PHP script to print Fibonacci series in PHP.

## What is Recursion?

In recursion, A function calls itself until the base condition is reached. Recursive code is much cleaner and shorter as compared to iterative code.

For better understanding you can my previous post on recursion and what’s the difference between recursion and iteration.

For practice, you can solve Objective Question on Recursion

### What is Fibonacci Series?

In Fibonacci series, the first two numbers are 0 and 1 and each subsequent number is the sum of previous two numbers.

0 ,1 , 1, 2, 3, 5, 8, 13, 21 ……………….

In mathematical terms, the Nth term of Fibonacci numbers is defined by the recurrence relation.

- fibonacci(N) = fibonacci(N – 1) + fibonacci(N – 2)
- whereas fibonacci(0) = 0 and fibonacci(1) = 1

## C Program to Print Fibonacci Series using Recursion

We have learned about Fibonacci series and it’s mathematical recurrence relation. Let’s write a C program to generate Fibonacci series using recursion.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | /* C Program to Print Fibonacci Series using Recursion */ #include <stdio.h> int fibonacci(int num){ if(num == 0) { return 0; } else if(num == 1) { return 1; } else { //recursive call return (fibonacci(num-1) + fibonacci(num-2)); } } main() { /* Assume we want to print first six number of Fibonacci series. */ int num; printf("Enter a number"); scanf("%d", &num); for(int i = 0; i < num; i++) { /* Call fibonacci function. */ printf(" %d ",fibonacci(i)); } } |

**Program Logic**

1. Return 0 if the input number is 0, 1 if the input number is 1.

2. If number is greater than 1 then **return func(n-1) + func(n-2)**. **func** is the name of a function.

**Explanation** – Suppose an input number is 4.

1 2 3 4 5 6 7 8 9 10 11 12 13 | /* When 4 is input, as per else condition. */ fibonacci(3) + fibonacci(2) /* fibonacci(3) and fibonacci(2), calls function */ (fibonacci(1) + fibonacci (2)) + (fibonacci(0) + fibonacci(1)) 1 + (fibonacci (1) + fibonacci (0) ) + 0 + 1 1 + 1 + 1 3 |

The Fourth element of Fibonacci series is 3. Similarly, other elements are printed in the same way.