/*
 * Figure 8.3  Program to Print a Table of Differences
 * Computes the mean and standard deviation of an array of data and displays
 * the difference between each value and the mean.
 */

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

#define kMaxItems  8  /* maximum number of items in list of data  */

int
main(void)
{
      double x[kMaxItems]; /* data list      */
      double mean;         /* mean (average) of the data    */
      double st_dev;       /* standard deviation of the data */
      double sum;          /* sum of the data                */
      double sum_sqr;      /* sum of the squares of the data */
      int    i;

      /* Gets the data */
      printf("Enter %d numbers separated by blanks or <return>s\n: ",
               kMaxItems);

      for  (i = 0;  i < kMaxItems;  i++)
      {
          scanf("%lf", &x[i]);
      }      

      /* Computes the sum and the sum of the squares of all data */
      sum = 0;
      sum_sqr = 0;
      for   (i = 0;  i < kMaxItems;  i++) 
      {
              sum += x[i];
              sum_sqr += x[i] * x[i];
      }

      /* Computes and prints the mean and standard deviation */
      mean = sum / kMaxItems;
      st_dev = sqrt(sum_sqr / kMaxItems - mean * mean);
      printf("The mean is %.2f.\n", mean);
      printf("The standard deviation is %.2f.\n", st_dev);

      /* Displays the difference between each item and the mean */
      printf("\nTable of differences between data values and mean\n");
      printf("Index       Item      Difference\n");
      for  (i = 0;  i < kMaxItems;  i++)
      {
             printf("%3d    %9.2f  %9.2f\n", i, x[i], x[i] - mean);
      }      

      return (0);
}