pr0634.cpp

来自「practice c++, it is from the book http:/」· C++ 代码 · 共 61 行

//  Programming with C++, Second Edition, by John R. Hubbard
//  Copyright McGraw-Hill, 2000
//  Problem 6.34 on page 146
//  Computing statistics

#include <cassert>   // defines the assert() function
#include <iostream>  // defines the cout object
using namespace std;
void print(double[],int);
double mean(double[],int);
double stdev(double[],int);  // from Problem 6.32

int main()
{ double x[] = { 2.5, 4.5, 6.3, 6.7, 7.2, 7.5, 7.8, 9.9 };
  int n=8;
  print(x,n);
  double m = mean(x,n);
  double s = stdev(x,n);
  cout << "mean = " << m << ", std dev = " << s << endl;
  for (int i=0; i<n; i++)
  { double z = (x[i] - m)/s;
    cout << "x[" << i << "] = " << x[i]
         << ", z[" << i << "] = " << z;
    if (z >= 1.5) cout << " = A" << endl;
    else if (z >= 0.5) cout << " = B" << endl;
    else if (z >= -0.5) cout << " = C" << endl;
    else if (z >= -1.5) cout << " = D" << endl;
    else  cout << " = F" << endl;
  }
}

void print(double x[], int n)
{ assert(n > 1);
  for (int i=0; i<n-1; i++)
    cout << x[i] << ", ";
  cout << x[n-1] << endl;
}

double mean(double x[], int n)
{ assert(n > 1);
  double sum=0;
  for (int i=0; i<n; i++)
    sum += x[i];
  return sum/n;
}

double stdev(double a[], int n)
{ assert(n > 1);
  double sum=0;
  for (int i=0; i<n; i++)
    sum += a[i];
  double mean = sum/n;  
  sum=0;
  double deviation;
  for (int i=0; i<n; i++)
  { deviation = a[i] - mean;
    sum += deviation*deviation;
  }
  return sqrt(sum/(n-1));  
}