C Program to show Fibonacci Sequence

This C program prints out the first Fibonacci series (sequence) of N numbers. In mathematics, the Fibonacci numbers are a sequence of numbers named after Leonardo of Pisa, known as Fibonacci. The first number of the sequence is 0, the second number is 1, and each subsequent number is equal to the sum of the previous two numbers of the sequence itself, thus creating the sequence 0, 1, 1, 2, 3, 5, 8, etc. The standard form of writing Fibonacci series is:

x_n = x_n-1 + x_n-2

where:

• x_n is term number “n”
• x_n-1 is the previous term (n-1)
• x_n-2 is the term before that (n-2)

Fibonacci Numbers

So this program prints the N numbers of Fibonacci series in C on the screen where N is the integer number entered by the user. This C program prints maximum of 50 Fibonacci numbers.

This program uses the following C Programming topics so go thorough these articles for a better understanding of the program:

• Operators in C Programming
• Loops and Decisions in C
• Functions in C Programming

#include <stdio.h>

int main(void) {
    //The number of Fibonacci numbers we will print
    int n; 
    // The index of Fibonacci number to be printed next 
    int i; 
    // The value of the (i)th Fibonacci number
    long current; 
    // The value of the (i+1)th Fibonacci number 
    long next; 
    // The value of the (i+2)th Fibonacci number 
    long twoaway; 

    printf("How many Fibonacci numbers do you want to compute? \n");
    scanf("%d", &n);
    
    if (n<=0 || n>50 ) {
        printf("The number should be positive and less than 51.\n");
    }
    else {
        printf("\n\n\tI \t Fibonacci(I) \n\t=====================\n");
        next = current = 1;
        for (i=1; i<=n; i++) {
            printf("\t%d \t %ld\n", i, current);
            twoaway = current+next;
            current = next;
            next = twoaway;
        }
    }
}

Output of the C Program

How many Fibonacci numbers do you want to compute? 
50


 I   Fibonacci(I) 
 =====================
 1   1
 2   1
 3   2
 4   3
 5   5
 6   8
 7   13
 8   21
 9   34
 10   55
 11   89
 12   144
 13   233
 14   377
 15   610
 16   987
 17   1597
 18   2584
 19   4181
 20   6765
 21   10946
 22   17711
 23   28657
 24   46368
 25   75025
 26   121393
 27   196418
 28   317811
 29   514229
 30   832040
 31   1346269
 32   2178309
 33   3524578
 34   5702887
 35   9227465
 36   14930352
 37   24157817
 38   39088169
 39   63245986
 40   102334155
 41   165580141
 42   267914296
 43   433494437
 44   701408733
 45   1134903170
 46   1836311903
 47   2971215073
 48   4807526976
 49   7778742049
 50   12586269025