factorial in C

int fact(int num)
{
    if(num<=0) return 1;

    return num * fact(num-1);
}

---------------------factorial.c---------------------
#include <stdio.h>
#include <stdlib.h>

int fact(int num)
{
    if(num<=0) return 1;

    return num * fact(num-1);
}

int main(int argc, char *argv[])
{
    int num = 0;

    if(argc < 2)
    {
        printf("usage: %s <number>\n", argv[0]);
        exit(0);
    }

    num = atoi(argv[1]);

    printf("factorial of %d is %d\n", num, fact(num));
    return 0;
}
-----------------------------------------------------