gauss for

#include<bits/stdc++.h>
using namespace std;
double x[100];
double y[100][100];
double find_p(double x1,int n)
{
    double temp;
    int k=1,s=4;
    if(n==0)
    {
        return 1;
    }
    for(int j=1; j<=n; j++)
    {
        if(j==1)
        {
            temp=x1;
            continue;
        }
        if(j==s)
        {
            s=s+2;
            if(j%2==0)
                k++;
        }
        if(j%2==0)
        {
            temp=temp*(x1-k);

        }
        else
        {
            temp=temp*(x1+k);

        }

    }

    return temp;

    }


int fact(int i)
{
   int f=1;
   for(int j=i;j>=1;j--)
   {
       f*=j;

   }
    return f;
}
int main()
{
   int n,p;
   int q;
   cout<<"enter the total element of x and y:";
   cin>>n;
   for(int i=0;i<n;i++)
   {
       cout<<"enter the element of x:";
       cin>>x[i];
       cout<<"enter the element of y[][]:";
       cin>>y[i][0];

   }
   for(int i=1;i<n;i++)
   {
       for(int j=0;j<n-i;j++)
       {
           y[j][i]=y[j+1][i-1]-y[j][i-1];

       }
   }
   cout<<"difference table:"<<endl;
   for(int i=0;i<n;i++)
   {
       cout<<x[i]<<"\t";
       for(int j=0;j<n-i;j++)
       {
           cout<<y[i][j]<<"\t";
       }
       cout<<endl;
   }
   if(n%2==0)
   {
       p=n/2;
       p=p-1;
       q=x[p];
   }
   else
   {
       p=n/2;
       q=x[p];
   }
    double value,x1;
    cout<<"enter desired value:";
    cin>>value;
    x1=(value-q)/(x[1]-x[0]);
    double sum=0;
    int k=1;
    cout<<q<<endl;

    for(int i=0;i<n;i++)
    {
        if(i==k+1)
        {
            k=k+2;
            p--;

        }

       sum=sum+(find_p(x1,i)*y[p][i])/fact(i);

    }
    cout<<"desired y="<<sum;

}