print random string with skip some character in ascii

I have a problem on generating random string from a function. I have use for loop in this case. In below code I have used ascii characters from 65 to 90. But I also want to include 48 to 57. Skipping 58 to 64. Is there any way to do this

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>

int main()
{

char s[30];
random_string(s, 6,65,90);
printf("\n%s\n", s);
return 0;
}

void random_string(char * string, unsigned length,int min,int max)
{
/* Seed number for rand() */
srand((unsigned int) time(0) + getpid());

/* ASCII characters 33 to 126 */
unsigned int num_chars = length - 1;
unsigned int i;
for (i = 0; i < num_chars; ++i)
{
  string[i] = rand() % (max - min + 1) + min;
}

string[num_chars] = '\0';

}

Please help me out