Simpel

strange floating point behaviour

3 posts in this topic

#1 ·  Posted

Hi.

I run this script:

Local $num = 0.7
While $num < 11
    $num += 0.1
    ConsoleWrite($num & @CRLF)
WEnd

Console output shows:

0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.99999999999999
6.09999999999999
6.19999999999999
6.29999999999999
6.39999999999999
6.49999999999999
6.59999999999999
6.69999999999999
6.79999999999999
6.89999999999999
6.99999999999999
7.09999999999999
7.19999999999999
7.29999999999999
7.39999999999999
7.49999999999999
7.59999999999999
7.69999999999999
7.79999999999999
7.89999999999999
7.99999999999999
8.09999999999999
8.19999999999999
8.29999999999999
8.39999999999999
8.49999999999999
8.59999999999999
8.69999999999999
8.79999999999998
8.89999999999998
8.99999999999998
9.09999999999998
9.19999999999998
9.29999999999998
9.39999999999998
9.49999999999998
9.59999999999998
9.69999999999998
9.79999999999998
9.89999999999998
9.99999999999998
10.1
10.2
10.3
10.4
10.5
10.6
10.7
10.8
10.9
11
11.1

After 5.9 follows 5.99999999999999 not 6. And later on it goes back from 9.99999999999998 to 10.1.

Why is that and how to avoid this. And with avoiding I don't mean:

ConsoleWrite(Round($num, 1) & @CRLF)

Regards, Conrad


SciTE = 3.6.2.0/full   AutoIt = 3.3.14.2   AutoItX64 = 0   OS = Win7Pro SP1   OSArch = X64   Language = 0407/german
H:\...\AutoIt3\SciTE   H:\...\AutoIt3   H:\...\AutoIt3\Include   H: = Network Drive

   88x31.png  Any of my own code posted anywhere on the forum is available for use by others without any restriction of any kind.

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#2 ·  Posted

Simpel,

Search the forum for "floating point arithmetic" - this subject has been covered many, many times before.

How to avoid? Do not use floats and try to stick with integers - for example with currency do the calculations in pennies/cents/whatever and convert back into pounds/dollars/slushniks when you have the final answer.

M23


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#3 ·  Posted

Thanks Melba,

should have known that. For those who want to know more about it there seems to be a good starting point here: http://floating-point-gui.de/

Conrad


SciTE = 3.6.2.0/full   AutoIt = 3.3.14.2   AutoItX64 = 0   OS = Win7Pro SP1   OSArch = X64   Language = 0407/german
H:\...\AutoIt3\SciTE   H:\...\AutoIt3   H:\...\AutoIt3\Include   H: = Network Drive

   88x31.png  Any of my own code posted anywhere on the forum is available for use by others without any restriction of any kind.

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