What is the Fibonacci Series?

The Fibonacci sequence is a mathematical series where each number is the sum of the two preceding numbers, starting from 0 and 1:

text (ISO Standard)
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F(0) = 0, F(1) = 1, F(n) = F(n-1) + F(n-2)

First 10 terms: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34

1. Iterative Approach (Recommended)

The iterative approach uses a simple loop with O(n) time complexity and O(1) auxiliary space:

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

void printFibonacciIterative(int n) {
    long long first = 0;
    long long second = 1;
    long long next;

    printf("Fibonacci Series (%d terms):\n", n);

    for (int i = 0; i < n; i++) {
        if (i <= 1) {
            next = i;
        } else {
            next = first + second;
            first = second;
            second = next;
        }
        printf("%lld ", next);
    }
    printf("\n");
}

int main() {
    int terms = 10;
    printFibonacciIterative(terms);
    return 0;
}

Expected Output

text (ISO Standard)
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Fibonacci Series (10 terms):
0 1 1 2 3 5 8 13 21 34 

2. Recursive Approach

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

long long fibonacci(int n) {
    if (n <= 0) return 0;
    if (n == 1) return 1;
    return fibonacci(n - 1) + fibonacci(n - 2);
}

int main() {
    int terms = 10;
    printf("Fibonacci Series via Recursion:\n");
    for (int i = 0; i < terms; i++) {
        printf("%lld ", fibonacci(i));
    }
    printf("\n");
    return 0;
}

Complexity Comparison

Related Tutorials & Examples

• Understand recursion in Functions in C Programming.
• Review loop syntax in C Programming Basics.
• Try more math examples like Prime Number Program in C.