How to use fmod and avoid precision issues

Question

I\'m going to boil this problem down to the simplest form:

Let\'s iterate from [0 .. 5.0] with a step of 0.05 and print out \'X\' for every 0.25 multipl

Answer 1

In cases where you always have the same fixed decimal fraction, simply multiply by up your loop counter (by 20 in this case). When you want to access it as a double, divide by 20. In effect, you are using a hidden exponent to keep your double an integer.

In the example, I use an integer for a loop counter, assuming it has the required precision.

for(int i=0; i<=100; i+=1) {
  if(i % 5 == 0)
    print 'X';
  double d = (double)i / 20.0;
  // use d
}

Answer 2

I'd solve this by simply not using floating point variables in that way:

for (int i = 0; i <= 500; i += 5) {
  double d = i / 100.0;  // in case you need to use it.
  if ((i % 25) == 0)
    print 'X';
}

They're usually problematic enough that it's worth a little extra effort in avoiding them.