Not getting the right output

[sparki]

Sorry for the numerous posts I made. As I'm new to C++, I really do need help. Hope you will understand. The center test failed to get the correct output but I already made a center function which I thought was correct and now I really do not know why it failed. Can anyone enlighten me? Thanks!

Output:
- Polygon::center test failed
5.91573 8.56946
1.93828 8.13865

class Object
{
public:

private:
	float d;
public:
	Object(float n) : d(n){}
struct PointType
{
	float x;
	float y;
	PointType( float x1,  float y1) :x(x1),y(y1){}
	PointType(){}
};
};
class Point :public Object 
{
 
private:
    PointType mpoint;
	
public:

    Point(const PointType& pt, float& y1) : mpoint(pt), Object(y1) {}
	
  	 Point center() 
	{
	     return *this;
	}
	  float x()
	{
		return mpoint.x2;

	}
	  float y()
	{
		return mpoint.y2;
	}
};
	
class Polygon :  public Point
{
private:
	Object::PointType *mpt;
	int msize;
	
public:
	   PointType& operator[](int index)  
	 {
		 return mpt[index];
	 }
	Polygon(PointType* points, int npoints, float depth)
	:  msize(npoints), mpt{new Object::PointType[npoints]}, Point(*mpt,depth){
		for(int i = 0; i < msize; ++i)
		{
		 mpt[i]  = points[i];
		}
	}
	Polygon center() 
	{
	     return *this;
	}
	 float x()
	{
		return mpt-> x2;
	}
	 float y()
	{
		return mpt-> y2;
	}
};

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <cmath>

const float EPSILON = 1e-5f;

bool is_near(float x, float y)
{
	return std::abs(x - y) < EPSILON;
}

float frand()
{
	return 10.0f * float(rand()) / float(RAND_MAX);
}

int main()
{
	srand(unsigned(time(0)));
	int count = 0;
	int max_count = 0;

	int max_index = 3 + rand() % 8;
	float* xs = new float[max_index];
	float* ys = new float[max_index];
	float depth = frand();
	float x = 0;
	float y = 0;
	Polygon::PointType* vertices = new Polygon::PointType[max_index];
	for (int index = 0; index < max_index; ++index)
	{
		xs[index] = frand();
		ys[index] = frand();
		vertices[index] = Polygon::PointType(xs[index], ys[index]);
		x += xs[index];
		y += ys[index];
		y += ys[index];
	}
	x /= static_cast<float>(max_index);
	y /= static_cast<float>(max_index);
	Polygon polygon(vertices, max_index, depth);
	delete[] vertices;
        if (is_near(polygon.center().x(), x) &&
		is_near(polygon.center().y(), y))
	{
		++count;
	}
	else
	{
		std::cout << "  - Polygon::center test failed" << std::endl;
	}
	std::cout <<polygon.center().x()<< " " << x <<std::endl;
		std::cout <<polygon.center().y()<< " " << y <<std::endl;

	++max_count;
}

[Peter87]

polygon.center() returns the first point in the list of points that makes up the polygon.

[sparki]

Thanks for the help. Anyway, I did try to put the first point. Is this the way to do it? becoz I am still not getting the correct output.

class Polygon :  public Point
{
private:
	Object::PointType *mpt;
	int msize;
	
public:
	   PointType& operator[](int index)  
	 {
		 return mpt[index];
	 }
	Polygon(PointType* points, int npoints, float depth)
	:  msize(npoints), mpt{new Object::PointType[npoints]}, Point(*mpt,depth){
		for(int i = 0; i < msize; ++i)
		{
		 mpt[i]  = points[i];
		}
	}

        Polygon center() 
	{
	     return *this;
	}
	 float x()
	{
		return mpt[0].x2;
	}
	 float y()
	{
		return mpt[0].y2;
	}
};

[Peter87]

My point is that polygon.center() gives you the first point which is not necessarily at the centre of the polygon. I have no idea what polygon.x() and polygon.y() is supposed to return (also the centre coordinates?).

I assume x2 and y2 are the same as x and y because x2 and y2 has not been declared anywhere.

I also don't think you should have two lines that do y += ys[index]; when calculating the centre y-coordinate.

[sparki]

main() can't be modified. So theres nothing I can do about it. x2 and y2 are the same as x and y. The center is the same as the first point as what you said so it is not necessarily the center. But why am I not getting the correct output? So frustrating.

[Peter87]

But why am I not getting the correct output? So frustrating.

The center is [...] not necessarily the center.

main() can't be modified. So theres nothing I can do about it.

Are you sure you haven't accidentally duplicated that line of code? It doesn't look right to me.

[sparki]

Oh.. yup you're right. It was accidentally duplicated by me.. Thanks Peter! However, the center function still does not work as it should. haiz~

[Peter87]

However, the center function still does not work as it should.

It's because you haven't implemented the center() function correctly.

[sparki]

Oh, What am I doing wrong with my center function? I am really not sure what else to do with the center function...

[Peter87]

As I have said earlier, the center() function returns the first point, not the center (average) of all points as it should.

[aten98]

hello can you help me? my output for standard derivation is incorrect. how to fix this ??

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

using namespace std;


int main()
{
int i,sum,sum3,sum4;
float mean,sd;
int a[101]={};
int sum2[101]={};
int b[101]={};
sum3=0;

int n;

int array[100]={0};//number of numbers must not more than 100
cout<<"This program will calculate mean and standard deviation for less 100"<<endl;
cout<<"How many numbers? " ;
cin>>n;

if (n<=100)
{
for (i=1; i<=n;i++)//the value must be positive or more than 1
{
cout<<"Please enter data number "<<i<<" : ";
cin >> a[i];
sum += a[i];
mean=sum/n;
b[i] += (a[i]-mean);
sum2[i]= pow(b[i],2);
sum3 = (sum3 + sum2[i]);
sum4 = (sum3/n);

}

sd = sqrt(sum4);
cout<<"Mean, x = "<<mean<<endl;
cout<<"standard deviation = "<<sd<<endl;
cout<<sum4<<endl;

}
else//less than 0 or negative value
{
cout<<"error";

cout<<endl<<endl;

}
}