Fibonacci in C

Welcome to the Fibonacci in C page! Here, you’ll find the source code for this program as well as a description of how the program works.

Current Solution

#include <stdio.h>
#include <errno.h>
#include <inttypes.h>
#include <string.h>

/*
 * This limit is chosen because fib(93) is the first number that is
 * still small enough to fit into a 64 bit integer.
 */
#define LIMIT 93

void fibonacci(int n)
{
    unsigned long long first = 0;
    unsigned long long second = 1;
    unsigned long long result = 0;

    for (int i = 1; i <= n; i++) {
        result = first + second;
        first = second;
        second = result;
        printf("%d: %llu\n", i, first);
    }
}

int main(int argc, char **argv)
{
    uintmax_t n;

    if (argc < 2 || strcmp(argv[1], "") == 0) {
        fprintf(stderr, "Usage: please input the count of fibonacci numbers to output\n");
        return 1;
    }

    errno = 0;
    n = strtoumax(argv[1], NULL, 10);
    if (n == 0 && strcmp(argv[1], "0") != 0 || (n == UINTMAX_MAX && errno == ERANGE)) {
        fprintf(stderr, "Usage: please input the count of fibonacci numbers to output\n");
        return 1;
    }

    if (n > LIMIT) {
        fprintf(stderr, "n cannot be larger than %d\n", LIMIT);
        return 1;
    }

    fibonacci(n);
    return 0;
}

Fibonacci in C was written by:

• Christoph Böhmwalder
• Jeremy Grifski
• Parker Johansen

If you see anything you’d like to change or update, please consider contributing.

Note: The solution shown above is the current solution in the Sample Programs repository as of Apr 18 2019 17:58:44. The solution was first committed on Oct 04 2018 20:05:30. As a result, documentation below may be outdated.

How to Implement the Solution

No ‘How to Implement the Solution’ section available. Please consider contributing.

How to Run the Solution

No ‘How to Run the Solution’ section available. Please consider contributing.