Question

So I have a simple for loop:

  double bg = 5.0;
  double f = 0.0;
  for(double i = 0; i <= bg; i += 1)
    {
        f = f + ((2 * i + 1)*0.1);

        if(i == bg)
        {
            System.out.printf ("%.1f" , f);
        }
    }

When I increment i with 1 for each itiration it works fine.
But when i do i += 0.1 it doesn’t print f.
Any ideas why?

Answer 1

You can not compare floats like that.

Usually equality of two floats(doubles) is checked with something like

if (Math.abs(i – bg) < 0.00001f) //0.00001f is very small value – almost zero, pick this value to suit your needs

For more look at http://www.cygnus-software.com/papers/comparingfloats/comparingfloats.htm

Your code should look like

  double bg = 5.0;
  double f = 0.0;
  for(double i = 0; i <= bg; i += 1)
    {
        f = f + ((2 * i + 1)*0.1);

        if (Math.abs(i - bg) < 0.00001f)
        {
            System.out.printf ("%.1f" , f);
        }
    }