/* Figure 7.2  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 MAX_ITEM  8  /* maximum number of items in list of data 	*/

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

        /* Gets the data                                         	 */
        printf("Enter %d numbers separated by blanks\n> ",
               MAX_ITEM);
	     for  (i = 0;  i < MAX_ITEM;  ++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 < MAX_ITEM;  ++i) {
              sum += x[i];
              sum_sqr += x[i] * x[i];
        }

        /* Computes and prints the mean and standard deviation    	*/
        mean = sum / MAX_ITEM;
        st_dev = sqrt(sum_sqr / MAX_ITEM - 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 < MAX_ITEM;  ++i)
             printf("%3d%4c%9.2f%5c%9.2f\n", i, ' ', x[i], ' ', x[i] - mean);

        return (0);
}

/*
Enter 8 numbers separated by blanks or <return>s
> 3
4 5  6  6 7 8 9
The mean is 6.00.
The standard deviation is 1.87.

Table of differences between data values and mean
Index       Item      Difference
  0         3.00         -3.00
  1         4.00         -2.00
  2         5.00         -1.00
  3         6.00          0.00
  4         6.00          0.00
  5         7.00          1.00
  6         8.00          2.00
  7         9.00          3.00
*/