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
    // If n is 0, the 0th Fibonacci number is 0
    if (n == 0) {
        return 0;
    } 
    // If n is 1, the 1st Fibonacci number is 1
    else if (n == 1) {
        return 1;
    } 
    // Step 2: Define the recursive step
    // For n > 1, the nth Fibonacci number is the sum of the (n-1)th and (n-2)th
    else {
        return fibonacci(n - 1) + fibonacci(n - 2);
    }
}

int main() {
    int n, i;

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

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

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

    return 0; // Indicate successful execution
}