RFID login system

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <windows.h>
#include <mysql/mysql.h>
#include "rs232.h"

#define BDRATE  9600
#define USERNAME    "toor"
#define PASSWORD    "password"
#define DATABASE    "test"
#define HOSTNAME    "192.168.1.6"


char *isValid (char *login) {
    MYSQL *c;
    MYSQL_RES *res;
    MYSQL_ROW row;
    int f,i;
    char *user;
    char query[128];
    c = mysql_init (NULL);
    if (mysql_real_connect (c,HOSTNAME,USERNAME,PASSWORD,DATABASE,0,NULL,0)==NULL) {
        return NULL;
    }
    else {
        sprintf (query, "SELECT username FROM users WHERE login = '%s'",login);
        mysql_query (c,query);
        res = mysql_store_result (c);
        f = mysql_num_fields (res);
        while (row = mysql_fetch_row (res)) {
            if (row[0]) {
                user = malloc (32);
                strcpy (user, row[0]);
                mysql_free_result (res);
                mysql_close (c);
                return user;

            }
        }
        mysql_free_result (res);
    }
    mysql_close (c);
    return NULL;
}

int findReader () {
    int i,c,len;
    char b[512];
    int outcpy = dup (1);
    fclose (stdout);
    for (c=0;c<16;c++) {
        if (!OpenComport (c,BDRATE)) {
            SendBuf (c,"i\r",2);
            for (i=0;i<10;i++) {
                len = PollComport (c, b, sizeof(b));
                if (len && !strncmp (b,"i\r\nMOD-RFID1356\r\n",17)) {
                    dup2 (outcpy, 1);
                    return c;
                }
                sleep (100);
            }
        }
        CloseComport (c);
    }
    dup2 (outcpy, 1);
    return -1;
}

char *readTag (int cport) {
    int i,len,d;
    char buf[512],tmp[64],req[64],ch,*ret,*ptr;
    SendBuf (cport, "r\r", 2);
    memset (buf,0,sizeof(buf));
    for (i=0;i<100;i++) {
        len = PollComport(cport, tmp, sizeof(tmp));
        if (len) {
            strncat (buf, tmp, len);
        }
        if (!strncmp (buf,"r\r\n\r\n-",6)) {
            strcpy (req, "c50,50,2023");
            strncat (req, buf+6, 16);
            strcat (req, "0004\r");
            memset (buf,0,sizeof(buf));
            for (d=0;d<3 && !strlen(buf);d++) {
                SendBuf (cport, req, strlen(req));
                for (d=0;d<100;d++) {
                    memset (tmp, 0, sizeof (tmp));
                    len = PollComport (cport, tmp, sizeof(tmp));
                    if (len) {
                        if (!strstr (tmp, "!e")) {
                            strncat (buf, tmp, len-1);
                            while (PollComport (cport, &ch, 1)) {
                                strncat (buf, &ch, 1);
                            }
                        }
                        break;
                    }
                    sleep (100);
                }
            }
            ptr = strstr (buf,"<00");
            if (ptr!=NULL) {
                ptr+=3;
                ret = malloc (strlen(ptr)-2);
                memset (ret,0,strlen(ptr)-2);
                strncpy (ret, ptr, strlen(ptr)-3);
                return ret;
            }
            return NULL;
        }
        sleep (100);
    }
    return NULL;
}

int main () {
    int cport;
    char ch;
    char buf[512];
    char *new, hash[33],*user;
    cport = findReader ();
    if (cport<0) {
        printf ("Reader not found!\n");
        CloseComport (cport);
        return 0;
    }

    new=NULL;
    while (new==NULL) {
        new = readTag (cport);
    }
    strncpy (hash, new, 32);
    hash[32]=0;
    user = isValid (hash);
    if (user!=NULL) {
        printf ("Welcome, %s!\n",user);
        free (user);
    }
    else {
        printf ("Login failed!\n");
    }
    free (new);

    CloseComport (cport);

    scanf ("%c",&ch);
    return 0;
}