Mysterious calculation error when multiply by 100

Question

The following script contains a very strange error. I want to check if a value is a positive integer. To do this, I multiply by 100 to enclose the value to decimal. If I tes

Answer 1

That's because javascript casts everything to a double internally. As a result, all calculations pick up some noise due to floating point inaccuracy: Floating point inaccuracy examples

One way to fix this issue, is to just round down to the nearest int after all intermediate calculations.

Answer 2

That's called numerical math. Computers do not operate on real numbers but on their approximation and this approximation brings rounding errors such as this one.

For 0.05, 0.06 and 0.08 you are lucky that these have an exact floating point representation on your PC. This is not the case of 0.07. Note that on a different PC/browser the result might be different.

For more info see the IEEE floating point format specification.