Rounding Off Issue

[amitmishra7]

Hi, I tried to make a simple calculator using this library. But I am facing an issue with a very simple expression. I tried to multiple 2.3 with 3 and the answer received was 6.8999999999999995. Rather it should have been simply 6.9.
I have used the below code

Expression exp = p.parse('2.3 * 3');
double val = exp.evaluate(EvaluationType.REAL, null);

The value of double returned here is 6.8999999999999995 instead of 6.9.

Another example is with the expression 2.1 * 3 which returned 6.300000000000001 instead of 6.3.

Same is the case with 52.2 % 2 which returned 0.20000000000000284 instead of 0.2

Can any one help me here?

[fkleon]

Hi @amitmishra7

I believe this is a similar issue as #27 and happens due to this library's use of 64 bit double-precision floating point numbers.
This is an issue that you will encounter in Dart and many other languages if you're not using big decimal representations.

I suggest to solve this you could round the results to the intended precision before presenting to the user/processing further.
This can be achieved by using Dart's toStringAsFixed method or writing your own rounding function.

For example:

void main() {
  double result = 2.3 * 3;
  print(result); // prints 6.8999999999999995
  String resultRounded = result.toStringAsFixed(5);
  print(resultRounded); // prints 6.90000
  double resultRoundedAsDouble = double.parse(resultRounded);
  print(resultRoundedAsDouble); // prints 6.9
}