Thread: Standard Deviaiton issue

I have been working on this for a few days now and I still can't wrap my head around arrays and filling in arrays to compute the Standard Deviation of an input file.

This is what I have:

Code:

#include <fstream>#include <iostream>
#include <cmath>


using namespace std;


double get_standard_dev( double Num [], int x );


const int size= 100;


int main ()
{
    int x, size;
    double Num[x];
    ifstream in_stream;


    cout << "We are going to find the standard deviation for the file stddev.dat" << endl;


    // Opens the input file.
    in_stream.open ( "stddev.dat" );


    // If the file fails to open it will close the program and output the statement.
    if ( in_stream.fail( ) )
    {
        cout << "Please check if the file is saved properly. It could not open." << endl;
    }


    cout << get_standard_dev( Num, size) << endl;


    return 0;
}


double get_standard_dev( double Num [], int x )
{
    double average, temp, mean;
    double sum = 0;
    int i;


    for( i = 0; i < x;i++ )
        {
        sum += Num[i];
        }


    average = sum / x;


    for( i = 0; i < x;i++ )


    {
    temp = Num[i] - average;
    sum += temp * temp;
    }


    mean = sum / x;


return sqrt(mean);
}

I don't quite understand where I am messing up in this program. It is outputting 1 and I can't figure out why. Can anyone point me in the right direction?

Code:

#include <fstream>
#include <iostream>
#include <cmath>
using namespace std;
double get_standard_dev( double Num [], int x );
const int size= 100;
int main ()
{
    int next;
    int count = 0;
    double Num[size];
    for(int i =0; i < size; i++)
    {
        Num[i]=0;
    }
    ifstream in_stream;
    cout << "We are going to find the standard deviation for the file stddev.dat" << endl;
    // Opens the input file.
    in_stream.open ( "stddev.dat" );
   // If the file fails to open it will close the program and output the statement.
if ( in_stream.fail( ) )
{
    cout << "Please check if the file is saved properly. It could not open." << endl;
    return 0; // you want to end the program here.  You can't calculate correctly if the file does not open
}
 while(in_stream >> next)
    {
       Num[count]=next;
       count++;
    }
    get_standard_dev ( Num , count );
// now read from in_stream into the Num[] array. Fill in x with the number of numbers in the file.
// now close the file
in_stream.close();
    return 0;
}
double get_standard_dev( double Num [], int x )
{
    double average, s;
    double sum = 0;
    int i;
    for( i = 0; i < x;i++ )
        {
        sum = sum + Num[i];
        }
    average = sum / x;
    sum = 0;
    for( i = 0; i < x; i++ )
    {
        s =pow((Num[i]-average),2);
        //cout << s<<" ";
        sum = sum + s;
    }
cout <<(sqrt (sum / x));
return 0;
}