re-faq1.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static int is_serial_valid(const char *user, const char *serial)
{    
    int i, total;
    for (i=0; i < strlen(user); i++) {
        total += user[i];
    }
    for (i=0; i < strlen(serial); i++) {
        total += serial[i];
    }
    return (((total + 17)*100057)%1871)==812;
}

int main(int argc, char *argv[])
{
    char *user;
    char *serial;
    if (argc<3) {
        printf("Usage: serial3 <user> <serial>\n");
        return 0;
    }
    user = argv[1];
    serial = argv[2];
    
    if (is_serial_valid(user, serial)) {
        printf("correct serial\n");
    } else {
        printf("incorrect serial\n");
    }
}