C program to print Fibonacci series

The Fibonacci series is a sequence of numbers where each number is the sum of the two preceding ones, typically starting with 0 and 1. It is a classic example often used to teach recursion and iterative programming techniques. In this article, we will explore how to write a C program to print the Fibonacci series up to a specified number of terms, n.

Understanding the Fibonacci Series

The following recurrence relation defines the Fibonacci series:

The first few terms of the Fibonacci series are:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

Algorithm to Generate Fibonacci Series

To generate the Fibonacci series up to n terms, we can use the following steps:

1. Input the number of terms n.
2. Initialize the first two terms of the series as 0 and 1.
3. Use a loop to calculate each subsequent term as the sum of the previous two terms.
4. Print each term as it is calculated.

Write a C program to print Fibonacci series

Here is the complete C program to print the Fibonacci series up to n terms:

#include <stdio.h>

int main() {
    int n, first = 0, second = 1, next, i;

    // Input the number of terms
    printf("Enter the number of terms: ");
    scanf("%d", &n);

    printf("Fibonacci series up to %d terms:\n", n);

    // Print the first two terms of the series
    if (n >= 1) printf("%d\n", first);
    if (n >= 2) printf("%d\n", second);

    // Calculate and print the rest of the terms
    for (i = 3; i <= n; i++) {
        next = first + second;
        printf("%d\n", next);
        first = second;
        second = next;
    }

    return 0;
}

Output

Enter the number of terms: 7
Fibonacci series up to 7 terms:
0
1
1
2
3
5
8

Explanation of the Code

1. Input the Number of Terms:
   • scanf("%d", &n); reads the number of terms n from the user.
2. Initialization:
   • The first two terms are initialized as first = 0 and second = 1.
3. Printing the First Two Terms:
   • The program checks if n is greater than or equal to 1 or 2 and prints the first two terms accordingly.
4. Calculating and Printing the Remaining Terms:
   • The for loop starts from the 3rd term and continues up to the ( n )-th term.
   • In each iteration, next is calculated as the sum of first and second.
   • The first and second values are then updated for the next iteration.

Example Runs

Example 1

Enter the number of terms: 5
Fibonacci series up to 5 terms:
0
1
1
2
3

Example 2

Enter the number of terms: 10
Fibonacci series up to 10 terms:
0
1
1
2
3
5
8
13
21
34