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

int get_random_4digit() {
  int random_4digit = 0;

  /* We must have 4 digits number - at least 1234 */
  while (random_4digit < 1000) {
    int digit = rand() % 9 + 1;  

    /* check if generated digit is not in the result */
    for (int number = random_4digit; number > 0; number /= 10) 
      if (number % 10 == digit) {
        digit = 0; /* digit has been found, we'll try once more */

        break;
      }

    if (digit > 0) /* unique digit generated, we add it to result */
      random_4digit = random_4digit * 10 + digit;
  }

  return random_4digit; 
}

int main() {
    int x = get_random_4digit();
    
    printf("%i", x);
    return 0;
}