Why can't all programming languages do this simple calculation?

Question

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<pre lang="PHP">echo 128.23 - (118.23 + 10);

Python

print(128.23 - (118.23 + 10))

JavaScript

console.log(128.23 - (118.23 + 10))

I tried in PHP, JavaScript and Python

All those calcs does not return 0 or 0.00, but return -2.842170943040401e-14

Somebody can explain to me why this happen?

What I have tried:

Actually i do not even know for where begin to understand because this have no sense to me

Posted 6-Feb-23 1:30am

Samuel Matos

Updated 6-Feb-23 2:59am

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Comments

CHill60 6-Feb-23 7:35am

This PDF from someone's degree course might help to explain https://people.cs.vt.edu/~asandu/Courses/CS3414/comp_arithm.pdf[^]

[no name] 6-Feb-23 13:28pm

You also have to appreciate what a "tiny" number e-14 is. With floating point, you generally ROUND to 0, or 1-4 decimals for presentation which gets rid of the problem. In other situations, accept negative numbers (as zero) if you find these small difference and which you can account for.

2 solutions

Solution 2

To add to what Richard has - rightly - said ...

Try it in C# using different numeric types: Double, Float, and Decimal:

C#

Console.WriteLine(128.23 - (118.23 + 10));
Console.WriteLine(128.23f - (118.23f + 10f));
Console.WriteLine(128.23m - (118.23m + 10m));

The results probably aren't what you expected:

-2.8421709430404E-14
-1.525879E-05
0.00

That's why .NET has a Decimal numeric type.

Posted 6-Feb-23 2:59am

OriginalGriff

Updated 6-Feb-23 3:00am

v2

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Richard MacCutchan · Accepted Answer · 2023-02-06T01:36:00

Solution 1

What Every Computer Scientist Should Know About Floating-Point Arithmetic[^]

Posted 6-Feb-23 1:36am

Richard MacCutchan

Comments

OriginalGriff 6-Feb-23 9:01am

:thumbsup:

Why can't all programming languages do this simple calculation?

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Why can't all programming languages do this simple calculation?