Polynomial FItting

#include<bits/stdc++.h>
using namespace std;

class PolynomialFit
{
    int i,j,k,n,N;
    double *x,*y;
public:
    void GaussEM(double B[][4],double a[]);
    void GetData();
    void Method();



};
void PolynomialFit::GetData()
{
        freopen("data.txt","r",stdin);
        cout<<"Enter the number of data of each variable"<<endl;
        cin>>N;
        x = new double[N];
        y = new double[N];
        cout<<"Enter all value of X : "<<endl;
        for (i=0;i<N;i++)
        cin>>x[i];
        cout<<"Enter the all value of Y : "<<endl;
         for (i=0;i<N;i++)
         cin>>y[i];
         cout<<"Enter the degree of the equation :"<<endl;
         cin>>n;
}

void PolynomialFit::Method()
    {
        double X[2*n+1];
        for (i=0;i<2*n+1;i++)
        {
            X[i]=0;
            for (j=0;j<N;j++)
                X[i]=X[i]+pow(x[j],i);
        }
        double B [3][4];
        double a[3];
        for (i=0;i<=n;i++)
            for (j=0;j<=n;j++)
                B[i][j]=X[i+j];
         double Y[n+1];
         for (i=0;i<n+1;i++)
         {
                Y[i]=0;
                for (j=0;j<N;j++)
                Y[i]=Y[i]+pow(x[j],i)*y[j];
        }
        for (i=0;i<=n;i++)
                B[i][n+1]=Y[i];
        n=n+1;

        GaussEM(B,a);

         cout<<"All Coefficient are below:\n";
        for (i=0;i<n;i++)
          cout<<"x^"<<i<<"="<<a[i]<<endl;
       cout<<"Final Equation is"<<endl;
      for (i=0;i<n;i++)
         cout<<"+"<<a[i]<<""<<"x^"<<i;
      cout<<endl;
    }

void PolynomialFit::GaussEM(double B[][4],double a[])
{
    for (i=0;i<n;i++)
        for (k=i+1;k<n;k++)
            if (B[i][i]<B[k][i])
                for (j=0;j<=n;j++)
                {
                    double temp=B[i][j];
                    B[i][j]=B[k][j];
                    B[k][j]=temp;
                }

    for (i=0;i<n-1;i++)
        for (k=i+1;k<n;k++)
            {
                double t=B[k][i]/B[i][i];
                for (j=0;j<=n;j++)
                    B[k][j]=B[k][j]-t*B[i][j];
            }
    for (i=n-1;i>=0;i--)
    {
        a[i]=B[i][n];
        for (j=0;j<n;j++)
            if (j!=i)
                a[i]=a[i]-B[i][j]*a[j];
        a[i]=a[i]/B[i][i];
    }
}
int main()
{
    PolynomialFit ob;
    ob.GetData();
    ob.Method();
return 0;
}