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JavaScript: Floating-point numbers

JavaScript doesn't distinguish between rational numbers (0.5) and natural numbers (10), both are numbers in JS (though other languages treat them differently). This means they can be used together in any operation:

3 * 0.5; // 1.5

However, due to their features, rational numbers are very different. As applied programmers, it wouldn't matter so much if it were not for one detail. Look at this example:

// Check this code in the [browser console](
0.2 * 0.2 // 0.04000000000000001

Multiplying two rational numbers has suddenly led to an imprecise result. Other programming languages deliver the same result. This happens due to the limits of computing power. The amount of memory, unlike the amount of numbers, is finite (an infinite amount of numbers requires an infinite amount of memory to store). In the case of natural numbers, this issue is solved by a simple upper bound (you can set the maximum number allowed). However, this is not impossible with rational numbers.

// Maximum possible integer

Rational numbers are not lined up in a continuous chain like integers, there's an infinite amount of numbers between 0.1 and 0.2. So now we have a big problem: how can we store rational numbers? Excellent question. There is a myriad of articles in the internet about memory organization in these cases. Moreover, there is even a standard describing how to do it correctly, and an overwhelming number of languages are based on this set of recommendations.

As developers, it's important to understand that operations with floating numbers are not precise (though precision can be adjusted using special tricks).


Compute and print the product of 0.39 and 0.22.

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

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