This Is my code. I'm getting strange results for the doubles.
#include <iostream>
using namespace std;

    double product = 0;
    double sumxy = 0;
    double sumx = 0;
    double sumy = 0;

void LLParams(const double x[], const double y[], int n, double &m, double &b)
{
for (int i = 0; i <= n; i++)
{
    product = x[i] * y[i];
    sumxy = sumxy + product;
    sumx = sumx + x[i];
    sumy = sumy + y[i];
}
{
    m = ((n*sumxy) - (sumx*sumy)) / ((n*sumx*sumx) - (sumx*sumx));
    b = (sumy - m*sumx) / n;
    cout << sumxy << "   " << sumx << "   " << sumy << endl;
}