I've written a program to calculate the chi-squared value using data given. However, I need to write it so that my program can account for not knowing how many lines are in the text file it is reading from. If I define my structure points as point thePoints[1000], (i.e. greater than the number of lines in the file) then the calculations do not work and i end up the 'nan' values. Here's my program:
#include<iostream>
#include<fstream>
#include<cmath>
using namespace std;
//define my own data structure
struct point {
double x;
double y;
double s;
double w;
double wx;
double wy;
double wxy;
double wxx;
double wmxcy;
};
//main program
int main() {
//array of point
point thePoints[11];
int i = 0;
//open a file to read in
ifstream myFile ("xys.data.txt");
//check if it opened successfully
if (myFile.is_open() ) {
//file is open
//read it in
while (!myFile.eof() ) {
//whilst we are not at the end of the file
myFile >> thePoints[i].x >> thePoints[i].y >> thePoints[i].s;
//increment i
i++;
}
//close the file
myFile.close();
}
// something went wrong
else {
cout << "Error opening file!\n";
exit(1);
}
// data is now in an array of point structures
//set the summation variables to zero - sets an initial value for the rest of the appropriate array to then be added onto
double Sw = 0;
double Swxx = 0;
double Swxy = 0;
double Swx = 0;
double Swy = 0;
double xsq = 0;
//create an array for w
for (int j = 0; j <= 10; j++){
thePoints[j].w = 1/(pow((thePoints[j].s),2));
//sum over all w i.e. create an array for Sw
Sw += thePoints[j].w;
//create an array for wx
thePoints[j].wx = (thePoints[j].w) * (thePoints[j].x);
//sum over all wx i.e. create an array for Swx
Swx += thePoints[j].wx;
//create an array for wy
thePoints[j].wy = (thePoints[j].w) * (thePoints[j].y);
//sum over all wy i.e. create an array for Swy
Swy += thePoints[j].wy;
//create an array for wxy
thePoints[j].wxy = (thePoints[j].w) * (thePoints[j].x) * (thePoints[j].y);
//sum over all wxy i.e. create an array for Swxy
Swxy += thePoints[j].wxy;
//create an array for wxx
thePoints[j].wxx = (thePoints[j].w) * (thePoints[j].x) * (thePoints[j].x);
//sum over all wxx i.e. create an array for Swxx
Swxx += thePoints[j].wxx;
}
printf("%6.2f, %6.2f, %6.2f, %6.2f, %6.2f\n", Sw, Swx, Swy, Swxy, Swxx);
//caluculate a value for D
double D = ((Sw * Swxx) - (Swx * Swx));
//calculate a value for m
double m = ((Sw * Swxy) - (Swx * Swy))/D;
//calculate a value for dm
double dm = sqrt(Sw/D);
//calculate a value for c
double c = ((Swy * Swxx) - (Swx * Swxy))/D;
//calculate a value for dc
double dc = sqrt(Swxx/D);
//calculate chi-squared value, xsq = Sw(((m * x) + c - y)^2)
for (int j = 0; j < i; j++){
thePoints[j].wmxcy = (thePoints[j].w * (pow(((m * thePoints[j].x) + c - thePoints[j].y),2)));
//sum over all chi-squared
xsq += thePoints[j].wmxcy;
}
//prints all of the results of the data
printf("The equation of the line for the data is y = %6.2f x + %6.2f.\n", m, c);
printf("The gradient, m, has an associated error of %6.2f.\n", dm);
printf("The y intercept, c, has an associated error of %6.2f.\n", dc);
printf("The data has a chi-squared value of %6.2f.\n", xsq);
return 0;
}
I have attached the input file.txt file
Any opinions would be much appreciated.