Ad:

C++ Discussion Thread
Marked Solved
Views: 4079

Sep 27th, 2006

variance calc incorrect why?

Expand Post »

#include <iostream>
#include<iomanip>
#include <cmath>
usingnamespace std;
int main()
{

char choice;
const int arraysize=20;
int num[arraysize];
do
{

cout<<"I will give you the Sum,Mean,Var & the Std Dev of any series of numbers?Y/N:"<<endl;
cin>>choice;
if(choice =='Y'||choice =='y')
{

cout<<"How many numbers will you enter? (up to 20)?"; cin>>num[arraysize];
for (int j=0;j<num[arraysize];j++)
{
cout<<"Enter Number"<<j+1<<":"; cin>> num[j];
}

cout << " You have entered the following:"<<endl;
for (j = 0; j < num[arraysize]; j++)
{

cout << num[j]<<" ";
}
int sum=0;
for (j=0;j<num[arraysize];j++)
sum+= num[j];
cout<<"\nThe Sum is "<<sum<<endl;
float mean= (sum/num[arraysize]);
cout << showpoint << fixed << setprecision (2);
cout<<"The Mean is "<<mean<<endl;
float var=((num[0]-mean)*pow(num[0]-mean,2) + (num[1]-mean)*pow(num[1]-mean,2) + + (num[2]-mean)*pow(num[2]-mean,2))/ (num[arraysize-1]);
cout << showpoint << fixed << setprecision (2);
cout<<"The Varience is " <<var<<endl;
float sqrtvar=sqrt(var);
cout << showpoint << fixed << setprecision (2);
cout<<"The Standard deviation is "<<sqrtvar<<endl;
}
}while(choice!='N'&& choice!='n');
return 0;

}

Similar Threads

Programs Identifying incorrect version of Windows! Help! in Windows NT / 2000 / XP
Incorrect Links to My Site in Site Layout and Usability

Sashar400

Reputation Points: 22

Solved Threads: 0

Newbie Poster

Offline

9 posts
since Aug 2006

Permalink

Sep 27th, 2006

Re: variance calc incorrect why?

And the question is?

andor

Reputation Points: 251

Solved Threads: 29

Posting Whiz in Training

Offline

274 posts
since Jun 2005

Permalink

Sep 27th, 2006

Re: variance calc incorrect why?

Click to Expand / Collapse Quote originally posted by Sashar400 ...

(Toggle Plain Text)
#include <iostream>
#include<iomanip>
#include <cmath>
usingnamespace std;
int main()
{ 

char choice;
int total_numbers  = 0 ;
const int arraysize=20;
int num[arraysize]; 
do
{

cout<<"I will give you the Sum,Mean,Var & the Std Dev of any series of numbers?Y/N:"<<endl;
cin>>choice; 
if(choice =='Y'||choice =='y')
{ 

cout<<"How many numbers will you enter? (up to 20)?";
// cin>>num[arraysize];  this is wrong it means entering value in 20th element
cin >> total_numbers ;  // this is correct way of accpeting single number
 for (int j=0; j < total_numbers; j++)
{
cout<<"Enter Number"<<j+1<<":"; cin>> num[j];
}

cout << " You have entered the following:"<<endl;
for (j = 0;  j < total_numbers; j++)
{
cout << num[j]<<" ";
}
int sum=0;
for (j=0; j <  total_numbers; j++)
sum+= num[j];
cout<<"\nThe Sum is "<<sum<<endl;
float mean= (sum/ total_numbers);
cout << showpoint << fixed << setprecision (2);
cout<<"The Mean is "<<mean<<endl;
float var=((num[0]-mean)*pow(num[0]-mean,2) + (num[1]-mean)*pow(num[1]-mean,2) + + (num[2]-mean)*pow(num[2]-mean,2))/ (num[arraysize-1]); 
cout << showpoint << fixed << setprecision (2);
cout<<"The Varience is " <<var<<endl;
float sqrtvar=sqrt(var);
cout << showpoint << fixed << setprecision (2);
cout<<"The Standard deviation is "<<sqrtvar<<endl;
}
}while(choice!='N'&& choice!='n');
return 0;

}
#include <iostream> #include<iomanip> #include <cmath> usingnamespace std; int main() { char choice; int total_numbers = 0 ; const int arraysize=20; int num[arraysize]; do { cout<<"I will give you the Sum,Mean,Var & the Std Dev of any series of numbers?Y/N:"<<endl; cin>>choice; if(choice =='Y'||choice =='y') { cout<<"How many numbers will you enter? (up to 20)?"; // cin>>num[arraysize]; this is wrong it means entering value in 20th element cin >> total_numbers ; // this is correct way of accpeting single number for (int j=0; j < total_numbers; j++) { cout<<"Enter Number"<<j+1<<":"; cin>> num[j]; } cout << " You have entered the following:"<<endl; for (j = 0; j < total_numbers; j++) { cout << num[j]<<" "; } int sum=0; for (j=0; j < total_numbers; j++) sum+= num[j]; cout<<"\nThe Sum is "<<sum<<endl; float mean= (sum/ total_numbers); cout << showpoint << fixed << setprecision (2); cout<<"The Mean is "<<mean<<endl; float var=((num[0]-mean)*pow(num[0]-mean,2) + (num[1]-mean)*pow(num[1]-mean,2) + + (num[2]-mean)*pow(num[2]-mean,2))/ (num[arraysize-1]); cout << showpoint << fixed << setprecision (2); cout<<"The Varience is " <<var<<endl; float sqrtvar=sqrt(var); cout << showpoint << fixed << setprecision (2); cout<<"The Standard deviation is "<<sqrtvar<<endl; } }while(choice!='N'&& choice!='n'); return 0; }

I think you gettting the fundamentals of programming wrong. Why you taking in the number of elements entered by the user into an array. Why not just use a simple int variable like "total_numbers".

I have made some changes in teh program, try running it now and see what you get. And also format your code a bit so it can be read by other people and put the code in the [code] tags.

Hope it helped ,bye.

Last edited by ~s.o.s~; Sep 27th, 2006 at 12:45 pm.

~s.o.s~

Super Moderator

Featured Poster

Reputation Points: 3233

Solved Threads: 719

Failure as a human

Offline

8,871 posts
since Jun 2006

Permalink

Sep 27th, 2006

Re: variance calc incorrect why?

same result

Sashar400

Reputation Points: 22

Solved Threads: 0

Newbie Poster

Offline

9 posts
since Aug 2006

Permalink

Sep 27th, 2006

Re: variance calc incorrect why?

See also http://www.daniweb.com/techtalkforums/thread56253.html
> usingnamespace std;
Now I don't know whether this is an endemic problem with your coding, but it should be using namespace std;, that is, there is a space in there.

Now maybe it's you or maybe it's some damn fool code colouring script you're running which is bugged to hell and back. Either way, it's not helpful to have to second guess what the difference is between what you posted and what we see.

Just post your code between tags, direct from your source code editor. We don't need colouring in a variable width font if the price is mangled code. Keep it nice and simple in a monospaced font.

Salem

Team Colleague

Reputation Points: 5862

Solved Threads: 950

Posting Sage

Offline

7,164 posts
since Dec 2005

Permalink

Sep 27th, 2006

Re: variance calc incorrect why?

I think you are getting the formulas for deviation and variace wrong.

See this code for reference;

C++ Syntax (Toggle Plain Text)
#include <iostream>
#include<iomanip>
#include <cmath>
using namespace std;
 
int main()
{
    float deviation, var ;
    char choice;
    int total_numbers  = 0 ;
    const int arraysize=20;
    int num[arraysize];
    do
    {
        cout<<"I will give you the Sum,Mean,Var & the Std Dev of any series of numbers?Y/N:"<<endl;
        cin>>choice;
        if(choice =='Y'||choice =='y')
        {
            cout<<"How many numbers will you enter? (up to 20)?";
            cin >> total_numbers ;  // this is correct way of accpeting single number
            for (int j=0; j < total_numbers; j++)
            {
                cout<<"Enter Number"<<j+1<<":"; cin>> num[j];
            }
            cout << " You have entered the following:"<<endl;
            for ( int j = 0;  j < total_numbers; j++)
            {
                cout << num[j]<<" ";
            }
 
            int sum=0;
            for (int j=0; j <  total_numbers; j++)
                sum+= num[j];
            cout<<"\nThe Sum is "<<sum<<endl;
            float mean= (sum/ total_numbers);
            cout << showpoint << fixed << setprecision (2);
            cout<<"The Mean is "<<mean<<endl;
 
            if (total_numbers > 1)
            {
                for (int i = 0; i < total_numbers; ++i )
                {
                    var += ((num [i] - mean) * (num [i] - mean)) ;
                }
                var /= (total_numbers - 1) ;
                deviation =sqrt(var);
            }
 
            else
            {
                var = 0.0 ;
                deviation = 0.0 ;
            }
            cout << showpoint << fixed << setprecision (2);
            cout<<"The Varience is " <<var<<endl;
            cout << showpoint << fixed << setprecision (2);
            cout<<"The Standard deviation is "<<deviation<<endl;
        }
    }
    while(choice!='N'&& choice!='n');
    return 0;
 
}
#include <iostream>
#include<iomanip>
#include <cmath>
using namespace std;

int main()
{
    float deviation, var ;
    char choice;
    int total_numbers  = 0 ;
    const int arraysize=20;
    int num[arraysize];
    do
    {
        cout<<"I will give you the Sum,Mean,Var & the Std Dev of any series of numbers?Y/N:"<<endl;
        cin>>choice;
        if(choice =='Y'||choice =='y')
        {
            cout<<"How many numbers will you enter? (up to 20)?";
            cin >> total_numbers ;  // this is correct way of accpeting single number
            for (int j=0; j < total_numbers; j++)
            {
                cout<<"Enter Number"<<j+1<<":"; cin>> num[j];
            }
            cout << " You have entered the following:"<<endl;
            for ( int j = 0;  j < total_numbers; j++)
            {
                cout << num[j]<<" ";
            }

            int sum=0;
            for (int j=0; j <  total_numbers; j++)
                sum+= num[j];
            cout<<"\nThe Sum is "<<sum<<endl;
            float mean= (sum/ total_numbers);
            cout << showpoint << fixed << setprecision (2);
            cout<<"The Mean is "<<mean<<endl;

            if (total_numbers > 1)
            {
                for (int i = 0; i < total_numbers; ++i )
                {
                    var += ((num [i] - mean) * (num [i] - mean)) ;
                }
                var /= (total_numbers - 1) ;
                deviation =sqrt(var);
            }

            else
            {
                var = 0.0 ;
                deviation = 0.0 ;
            }
            cout << showpoint << fixed << setprecision (2);
            cout<<"The Varience is " <<var<<endl;
            cout << showpoint << fixed << setprecision (2);
            cout<<"The Standard deviation is "<<deviation<<endl;
        }
    }
    while(choice!='N'&& choice!='n');
    return 0;

}

Maybe for the formula you should look here;

http://www.cs.mtu.edu/~shene/COURSES/cs201/NOTES/chap08/means-8.html

Hope it helped, bye.

~s.o.s~

Super Moderator

Featured Poster

Reputation Points: 3233

Solved Threads: 719

Failure as a human

Offline

8,871 posts
since Jun 2006

Permalink

Sep 28th, 2006

Re: variance calc incorrect why?

Like what ~S.O.S~ have said. The formula for variance in your coding is wrong. The formula of a variance is like this. Take the example that user input 3 numbers 1,2,3 and the mean is 2

(1-2)^2+(2-2)^2+(3-2)^2)/3. Your variance formula seems to be fixed up to 3 numbers. Therefore, the answer will be incorrect no matter how many numbers are input. Below is one of the way to correct the calculation.

(Toggle Plain Text)

float var=0.0;
for (j=0;j<num[arraysize];j++)
{
var += (float)pow(num[j]-mean,2);
}
cout << "array=" << num[arraysize] << " Var=" << var << endl;
var /= num[arraysize];

Hope it helps.

Last edited by rinoa04; Sep 28th, 2006 at 6:01 am.

rinoa04

Reputation Points: 52

Solved Threads: 4

Junior Poster in Training

Offline

84 posts
since Sep 2006

This thread is solved

Either the thread starter or a moderator has marked this thread as solved. You can most likely trust the responses and answers given. There is most likely no reason for any further responses to be posted here. If you have a related question, please start a new thread in this forum instead.

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in C++ Forum Timeline: Communication Between C++, TCL

Next Thread in C++ Forum Timeline: optimize code

DaniWeb Message

Cancel Changes

User Name
Password