Factorial in C

Welcome to the Factorial 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 <stdint.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.h>

int uint64_overflow(long, long);

int main (int argc, char *argv[])
{
    long n;
    char *endptr;
    uint64_t result = 1;
    long i;

    /* Correct nmber of args? */
    if (argc != 2) {
        printf("Usage: please input a non-negative integer\n");
        exit(0);
    }

    /* Convert argument to number */
    errno = 0;
    n = strtol(argv[1], &endptr, 10);
    if ((errno == ERANGE && (n == LONG_MAX || n == LONG_MIN))
            || (errno != 0 && n == 0)) {
        perror("strtol");
        exit(1);
    }

    if (endptr == argv[1] ||
            !(*endptr == '\0' || *endptr == '\n') ||
            n < 0) {
        fprintf(stderr, "Usage: please input a non-negative integer\n");
        exit(1);
    }

    /* For non-zero numbers, compute factorial */
    if (n) {
        for (i = 1; i <= n; i++) {
            if (uint64_overflow(result, i)) {
                printf("Results overflowed\n");
                exit(1);
            }

            result *= i;
        }
    }

    /* Priunt result */
    printf("%ld\n", result);

    return 0;
}

/*
 * Detects overflow from 64-bit multiplication.
 *
 * Returns 1 if an overflow occurs, 0 if not
 */
int uint64_overflow(long a, long b) {
    uint64_t x;
    uint64_t b_64;

    x = a * b;
    b_64 = b;

    return (a != 0 && x / a != b_64) ? 1 : 0;
}

Factorial in C was written by:

• Bharath
• clarkimusmax

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 Oct 16 2019 15:14:04. The solution was first committed on Oct 26 2018 17:34:42. As a result, documentation below may be outdated.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.