Statistics

#include <stdio.h>
int main(void) {
  int i, n;
  double x[BUFSIZ], y[BUFSIZ], sumx, sumy, sumxx, sumxy, aa, a0, a1;
  sumx = sumy = sumxx = sumxy =0.;
  printf("n = ");
  scanf("%d", &n);

  printf("input x y:\n");
  for (i = 0; i < n; i++) {
    printf("%d ? ", i);
    scanf("%lf%lf", &x[i], &y[i]);
  }

  for (i = 0; i < n; i++)
    sumx += x[i];

  for (i = 0; i < n; i++)
    sumy += y[i];

  for (i = 0; i < n; i++)
    sumxx += x[i] * x[i];

  for (i = 0; i < n; i++)
    sumxy += x[i] * y[i];

  aa = n * sumxx - sumx * sumx;
  a0 = (sumxx * sumy - sumx * sumxy) / aa;
  a1 = (n * sumxy - sumx * sumy) / aa;
  printf("a0 = %g\n", a0);
  printf("a1 = %g\n", a1);
  return 0;
}