/* dice: Gather statistics about rolling
 * two dice.  A Monte Carlo simulation using
 * the random number generator rand()
*/
#include <stdio.h>   /* for the input/output */
#include <stdlib.h>  /* for rand and srand */
#include <time.h>    /* for time */

void initarray(int d[]);
void printarray(int d[]);
void printstar(int n);
void fancyprint(int d[]);
int roll(void);
int numrolls;

int main(void) {

   int d[13]; /* 2-12 hold num of rolls */
   int i;     /* loop variable */
   int starttime = time(NULL); /* clock time */
   srand((long)starttime); /* initialize RNG */
   printf("Enter # of rolls ---> ");
   scanf("%i", &numrolls); /* need & on variable */
   initarray(d);
   printf("Total rolls: %1d\n\n", numrolls);
   for (i = 0; i < numrolls; i++) /* simulation loop */
      d[roll() + roll()]++;
   printarray(d);
   fancyprint(d);
   printf("Elapsed time: %ld seconds\n",
      time(NULL) - starttime); /* current - initial */
   return 0;
}

/* initarray: initialize statistic array */
void initarray(int d[]) {
   int i;
   for (i = 2; i < 13; i++)
      d[i] = 0;
}

/* printarray: print each num of rolls */
void printarray(int d[]) {
   int i;
   double e[] = {0, 0,  /* array of frequencies */
      1.0/36.0, 2.0/36.0, 3.0/36.0, 4.0/36.0,
      5.0/36.0, 6.0/36.0, 5.0/36.0, 4.0/36.0,
      3.0/36.0, 2.0/36.0, 1.0/36.0};
   printf("Sum  Times   Frequency");
   printf("      Exact    Diff\n\n");
   for (i = 2; i < 13; i++)
      printf("%2d %7d %11.7f %10.7f %8.4f\n",
        i,
        d[i],
        (double)d[i]/numrolls*100.0,
        e[i]*100.0,
        ((double)(d[i]) -
           e[i]*numrolls)/numrolls*100.0);
}

/* printstar: print n stars */
void printstar(int n) {
   while (n > 0) {
      printf("*");
      n--;
   }
}

/* fancyprint: print bar graph */
void fancyprint(int d[]) {
   int i;
   printf("\n");
   for (i = 2; i < 13; i++) {
      printf("Sum:%3d |", i);
      printstar(300*d[i]/numrolls);
      printf("\n");
   }
   printf("\n");
}

/* roll: simulate rolling a die */
int roll(void) {
   return (int) (6.0*(rand()/(double)RAND_MAX) + 1.0);
}