Fibonacci in C

Published on 28 April 2022 (Updated: 25 September 2022)

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:

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 As a result, documentation below may be outdated.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

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