Objective-C - Get number of decimals of a double variable

Question

Is there a nice way to get the number of decimals of a double variable in Objective-C? I am struggling for a while to find a way but with no success.

For example 231.44232000 should return 5.

Thanks in advance.

Why should that number return 5? It really may be 231.4423200016 when you look at all the digits. — Hot Licks, Nov 28 '11 at 01:35

Graham Perks · Accepted Answer · 2014-12-27T16:57:14.783

4

You could, in a loop, multiply by 10 until the fractional part (returned by modf()) is really close to zero. The number of iterations'll be the answer you're after. Something like:

int countDigits(double num) {
  int rv = 0;
  const double insignificantDigit = 8;
  double intpart, fracpart;
  fracpart = modf(num, &intpart);
  while ((fabs(fracpart) > 0.000000001f) && (rv < insignificantDigit)) {
    num *= 10;
    rv++;
    fracpart = modf(num, &intpart);
  }

  return rv;
}

edited Dec 27 '14 at 16:57

answered Nov 28 '11 at 04:21

Graham Perks

23,007
8
61
83

1

This is what I needed. But you forgot to put fracpart = modf(num, &intpart); inside the while. – CristiC Nov 28 '11 at 08:21

score 1 · Answer 2 · answered Nov 28 '11 at 01:29

Is there a nice way to get the number of decimals of a double variable in Objective-C?

No. For starters, a double stores a number in binary, so there may not even be an exact binary representation that corresponds to your decimal number. There's also no consideration for the number of significant decimal digits -- if that's important, you'll need to track it separately.

You might want to look into using NSDecimalNumber if you need to store an exact representation of a decimal number. You could create your own subclass and add the ability to store and track significant digits.

Objective-C - Get number of decimals of a double variable

2 Answers2

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