Print first N numbers in BASE62

I would like to print first N numbers in BASE62 encoding. What's wrong in my code?

const char ALPHABET[63] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

int main(void) {
    int N = 50;
    for (int i = 0; i < N; i++) {
        int base62 = ALPHABET[i % 62];
        printf("Base 62: %s\n", (char*)base62);
    }
}

You need to print out string representing the number in base62. For N >= 62, you will have a multi-character string. First, you would need to count the number of digits in the base62 representation and then display character-by-character.

For that, you need to something like this-

// Count the number of characters the number will need
int num_digits(int num) {
   int count=0;
   while(num > 0) {
      num /= 62;
      count++;
   }
   if(count == 0)
      count = 1;
   return count;
}

int main() {
   const char ALPHABET[63] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
   int i, N=100;
   char STR[10];

   for (i = 0; i < N; i++) {
      int num = i;
      int digits = num_digits(num);
      STR[digits] = '\0';

      while(num > 0) {
         char base62 = ALPHABET[num % 62];
         STR[--digits] = base62;
         num /= 62;
      }

      if(i == 0)
         STR[--digits] = ALPHABET[0];
      printf("%s\n", i, STR);
   }
}