//
// standdev.cpp
//
// This program reads up to maxLength integers
// into an array and computes their standard
// deviation.
//

#include <iostream.h>
#include <math.h>

//
// maxLength is the most integers the program can manage.
//
const int maxLength = 20;

int fillArray(int A[]);
double averageArray(int A[], int length);
double standardDevArray(int A[], int length, double average);
double square(double number);

int main()
{
  int A[maxLength];
  int length;
  double average;
  double standardDeviation;
  
  length = fillArray(A);
  average = averageArray(A, length);
  standardDeviation = standardDevArray(A, length, average);
  cout << "The standard deviation of the data set is "
       << standardDeviation << endl;

  return 0;
}

//
// fillArray fills the array A with up
// to maxLength integers.  It stops 
// prompting when maxLength numbers 
// have been entered or the user enters 0.
// It returns the number of integers
// actually entered.
//
int fillArray(int A[])
{
  int index = 0, enteredValue;

  cout << "Please enter a positive value (0 to stop): ";
  cin >> enteredValue;

  while (index < maxLength && enteredValue != 0) {
  	A[index] = enteredValue;
  	index++;
  	cout << "Please enter a positive value (0 to stop): ";
    cin >> enteredValue;
  }
  
  return index;
}

//
// averageArray computes the average of 
// the integers in the array A, ie,
// the values in array locations A[0] to 
// A[length-1].
//
double averageArray(int A[], int length)
{
  int index;
  int sum = 0;
  
  for (index = 0; index < length; index++) {
    sum += A[index];
  }
  
  return sum / double(length);
}

//
// standardDevArray computes the standard
// deviation of the integers in the array A, 
// given the average of those values.
//
double standardDevArray(int A[], int length, double average)
{
  int index;
  double sum = 0;
  
  for (index = 0; index < length; index++) {
    sum += square(A[index] - average);
  }
  
  return sqrt(sum);
}

//
// square returns the square of its
// parameter.
//
double square(double number)
{
  return number * number;
}