Example: Fibonacci Series using Recursion in C

// Fibonacci Series using Recursion
#include <stdio.h>

// Function to calculate the nth Fibonacci number recursively
int fibonacci(int n) {
    // Step 1: Define base cases for the recursion
    // The 0th Fibonacci number is 0
    if (n == 0) {
        return 0;
    } 
    // The 1st Fibonacci number is 1
    else if (n == 1) {
        return 1;
    } 
    // Step 2: Recursive step for n > 1
    // The nth Fibonacci number is the sum of the (n-1)th and (n-2)th numbers
    else {
        return fibonacci(n - 1) + fibonacci(n - 2);
    }
}

int main() {
    int terms, i;

    // Step 3: Prompt user for the number of terms
    printf("Enter the number of terms for the Fibonacci series: ");
    scanf("%d", &terms);

    // Step 4: Validate input
    if (terms < 0) {
        printf("Please enter a non-negative number of terms.\n");
        return 1; // Indicate an error
    }

    // Step 5: Print the series
    printf("Fibonacci Series: ");
    for (i = 0; i < terms; i++) {
        printf("%d ", fibonacci(i)); // Call the recursive function for each term
    }
    printf("\n");

    return 0;
}