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enum {len = 12};
char id[len];  /* id will hold the ID, starting with 
                * the characters "ID" followed by a 
                * random integer */
int r;
int num;
/* ... */
r = rand();  /* generate a random integer */
num = snprintf(id, len, "ID%-d", r);  /* generate the ID */
/* ... */

enum {len = 12};
char id[len];  /* id will hold the ID, starting with 
                * the characters "ID" followed by a 
                * random integer */
int r;
int num;
/* ... */
time_t now = time(NULL);
if (now == (time_t) -1) {
  /* handle error */
}
srandom(now);  /* seed the PRNG with the current time */
/* ... */
r = random();  /* generate a random integer */
num = snprintf(id, len, "ID%-d", r);  /* generate the ID */
/* ... */

#include<Wincrypt.h>

HCRYPTPROV hCryptProv;
union {
    BYTE bs[sizeof(long int)];
    long int li;
} rand_buf;

if (!CryptGenRandom(hCryptProv, sizeof(rand_buf), &rand_buf) {
    /* Handle error */
} else {
    printf("Random number: %ld\n", rand_buf.li);
}