It doesn't return a correct result...

Hi,

I'm doing the first exercise on struct. I can't figure out why it doesn't return a correct result for median. It always rounds it up... Say if I input 1 2 3 4, it returns the median == 3, not 2.5, even though it uses type double. Could you please help? Also, could you please help suggest a bit of improvement on the program? I'm learning about struct/class and this exercises asks me to practice using struct...

Code:

// Exercise 8.12
#include "std_lib_facilities.h"
/*
	Write a function that finds the smallest & the largest element of vector
	argument and also compute the mean and the median. Do not use global variables.
	Either return a struct containing results or pass them back through reference
	arguments. Which one do you prefer, and why?

*/

struct stats {
	vector<double> v;
	double smallest, largest, median;
	double fmean(vector<double>& v);
	double fmedian(vector<double>& v);
	double fsmallest(vector<double>& v);
	double flargest(vector<double>& v);
};

int main()
try {
	stats mystats;
	vector<double> v;
	double x;
	cout << "Enter some elements for a vector: \n";
	while (cin >> x)
		v.push_back(x);
	cout << "Here are some summary statistics: \n";
	cout << "Smallest: " << mystats.fsmallest(v) << '\n';
	cout << "Largest: " << mystats.flargest(v) << '\n';
	cout << "Mean: " << mystats.fmean(v) << '\n';
	cout << "Median: " << mystats.fmedian(v) << '\n';
	
}
catch (runtime_error e) {
	cout << e.what();
}

double stats::fsmallest(vector<double>& v)
{
	smallest = v[0];
	for (unsigned int i = 0; i < v.size(); ++i) {
		if (v[i] < smallest)
			smallest = v[i];
	}
	return smallest;
}

double stats::flargest(vector<double>& v)
{
	largest = v[0];
	for (unsigned int i = 0; i < v.size(); ++i) {
		if (v[i] > largest)
			largest = v[i];
	}
	return largest;
}

double stats::fmean(vector<double>& v)
{
	double sum = 0;
	for (unsigned int i = 0; i < v.size(); ++i) {
		sum += v[i];
	}
	return sum / v.size();
}

double stats:: fmedian(vector<double>& v)
{
	sort(v.begin(), v.end());
	median = 0;
	for (unsigned int i = 0; i < v.size(); ++i) {
		if (v.size()%2==0)
			median = (v[v.size()/2] + v[v.size()/2-1])/2;
		median = v[v.size()/2];	
	}
	return median;
}

Code:

if (v.size()%2==0)
  median = (v[v.size()/2] + v[v.size()/2-1])/2;
median = v[v.size()/2];

Perhaps you intended to place an else in there somewhere?

Originally Posted by ctrl_freak

Perhaps you intended to place an else in there somewhere?

Thanks a lot, ctrl_freak. I should have put else just before median... Thanks for helping

I want to ask what "std_lib_facilities.h" is ? I can't find it in head files. I use the ubuntu OS.

Originally Posted by okgays

I want to ask what "std_lib_facilities.h" is ? I can't find it in head files. I use the ubuntu OS.

It's a header file used in the new book by Bjarne Stroustrup. I'm learning C++ from this book, so I copy it & use it in every program.

>I want to ask what "std_lib_facilities.h" is ?
http://www.stroustrup.com/Programmin...b_facilities.h