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danielmohr91

For Loop issue

7 posts in this topic

I'm terribly confused. I've got a simple "for" loop. I changed the increment to .1, and suddenly the loop never counts up to the max. For example,

For $i = 0 To $i = 100 Step .1 
ConsoleWrite($i & @LF) 
Next

outputs this:

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

shouldn't it go from 0 to 100 in .1 steps. ie, after 1 is 1.1 1.2 1.3 and so on until it reaches 100?

Also, it has trouble with negative numbers. ie, using -5 to 5 step 1 it will print

-5

-4

-3

-2

-1

0

and stop at zero?! I'm so confused. I want to count in decimal steps from -5 to 5, but I can't do either, even separately. Am I doing something wrong, or is this simply a limitation of the language?

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#2 ·  Posted (edited)

danielmohr91,

Go and read the Help file page for For again and check the syntax. :)

You might find that this runs as you want:

For $i = 0 To 100 Step .1
ConsoleWrite($i & @LF)
Next

Spot the difference. ;)

M23

Edit: But do not be surprised if some of the numbers are not exactly 0.1 apart. That is a limitation of floating point number representation, not an Autoit bug! ;)

Edited by Melba23

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Something al little odd about the ouput for me

22.1

22.2

22.3

22.4

22.5000000000001

22.6000000000001

22.7000000000001

22.8000000000001

22.9000000000001

23.0000000000001

23.1000000000001

23.2000000000001

23.3000000000001

23.4000000000001

23.5000000000001

23.6000000000001

23.7000000000001

23.8000000000001

23.9000000000001

24.0000000000001

It does make it back to normal, then goes ski-wiff again.


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#4 ·  Posted (edited)

Something al little odd about the ouput for me

....

It does make it back to normal, then goes ski-wiff again.

Nothing odd about this as this is simply how computers handle floating point numbers (in sum, without complete accuracy).

Please have a look here for more on this subject: What Every Computer Scientist Should Know About Floating-Point Arithmetic

I'm not sure how AutoIt does its for loops internally, but I know that in Java and C, if you are looping with a floating point index such as a double, your stop test should always use relational operator such as >= or <= and not just the equivalence operator, because it's all too easy for one floating point number to not be 100% equal to another even though logic tells you that they should be equal.

Edited by Fubarable

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Melba

You are right ! c'est "ballot" comme erreur ! Posted Image


AutoIt 3.3.14.2 X86 - SciTE 3.6.0WIN 8.1 X64 - Other Example Scripts

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danielmohr91,

Go and read the Help file page for For again and check the syntax. ;)

You might find that this runs as you want:

For $i = 0 To 100 Step .1
ConsoleWrite($i & @LF)
Next

Spot the difference. :)

M23

Edit: But do not be surprised if some of the numbers are not exactly 0.1 apart. That is a limitation of floating point number representation, not an Autoit bug! :P

Ha he. Thanks man. Wow, I feel like an idiot. I've been teaching myself JAVA and C++, and now coming back to AutoIt is the most unnatural thing. I keep mixing up the syntax. Things like declaring types for variables, and putting a semi-colon after every line lol. Thanks SO much for your help ;)

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