Why does the 3rd Loop become random numbers? C Programming

Question

/*
Output should reflect as follows:
Number of Engine Size: 5
  x Values: Corresponding Values
      1.5 , 110
      2.0 , 130
      2.4 , 245
      3.0 , 290
      3.6 , 310

1st Round: m = 11.996, c = 4.34, MSE = 53845
2nd Round: m = 22.145, c = 7.993, MSE = 38827.381
3th Round: m = 30.732, c = 11.066, MSE = 28091.485
4th Round: m = 37.999, c = 13.648, MSE = 20415.483
*/

#include <stdio.h>
#include <math.h>
#define MAXSIZE 100
float x[MAXSIZE], y[MAXSIZE], pred_y[MAXSIZE];
double m, c, Dm, Dc, MSE;

void predy (float m, float c, int times)
{
  int i;
  for (i = 0; i < times; i++)
    {
      pred_y[i] = m * x[i] + c;
    }
}

float calc_dm (int times)
{
  int i;
  float sum, Dm;
  double dm[MAXSIZE];
  for (i = 0; i < times; i++)
    {
      dm[i] = x[i] * (y[i] - pred_y[i]);
    }
  for (i = 0; i < times; i++)
    {
      sum += dm[i];
    }
  Dm = (-2 / (float)times) * sum;
  return Dm;
}

float calc_dc (int times)
{
  int i;
  float sum, Dc;
  double dc[MAXSIZE];
  for (i = 0; i < times; i++)
    {
      dc[i] = (y[i] - pred_y[i]);
    }
  for (i = 0; i < times; i++)
    {
      sum += dc[i];
    }
  Dc = (-2 / (float)times) * sum;
  return Dc;
}

float calc_MSE (int times)
{
  int i;
  double e[MAXSIZE];
  double sum = 0.0;
  for (i = 0; i < times; i++)
    {
      e[i] = (y[i] - pred_y[i]) * (y[i] - pred_y[i]);
    }
  for (i = 0; i < times; i++)
    {
      sum = sum + e[i];
    }
  MSE = sum / 5.0;
  return MSE;
}

int main() {
  int i, times,j;
  double pred_y[MAXSIZE];
  float n = 0.01;
  printf("Enter the number of Engine Size to be calculalted: ");
  scanf("%d", &times);
  for (i = 0; i < times; i ++)
    {
      printf("Enter the Engine Size for #%d: ", i + 1);
      scanf("%f", &x[i]);
      printf("Enter the corresponding CO2 Emission: ");
      scanf("%f", &y[i]);
    }
  
  for (j = 0; j < 5 ; j++)
  {
  predy(m, c, times);
  Dm = calc_dm(times);
  Dc = calc_dc(times);
  MSE = calc_MSE(times);
  m = m - n * Dm;
  c = c - n * Dc;
  m = round(m * 1000)/ 1000;
  c = round(c * 1000)/ 1000;
  MSE = round(MSE * 1000)/ 1000;
  printf ("Value of M: %.3f\n", m);
  printf ("Value of C: %.3f\n", c);
  printf ("Value of MSE: %.3f\n", MSE);
    }
  return 0;
}

Answer 1

I'm not sure about your calculations, but line 81 is definitely wrong as it is prone to read memory garbage. It should be this instead:

for (j = 0; j < times ; j++)

Actually, if you're calculating 5 consecutive predictions, your code may be fine.

I have no idea what you're calculating. Maybe your formulas are wrong? DC, DM, MSE? They mean nothing to me.

Comments

I am thinking why do u need these formulas for?