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For loop unexpected end value

Posted on 2008-10-29
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Last Modified: 2013-12-17
Hi, When experimenting with a for loop in c# I have an unexpected final value. The first code loop below shows an expected result with the values 0 - 1 printed to the output window in steps of 0.1. However the second example ends with a value of 0.95! Other step values such as 0.2, 0.25 work ok and ends on 1. But for some reason any step values below 0.1 don't end on 1, such as 0.05, 0.025, 0.01 etc.

Any explanation for this would be greatly appreciated. plus how I can make sure it always ends on 1 assuming the step value is entirely divisible into 1 with no remainder.
for (double i = 0; i <= 1; i += 0.1)
{
   Debug.WriteLine(i);
}
 
for (double j = 0; j <= 1; j += 0.05)
{
   Debug.WriteLine(j);
}

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Question by:dg_dibs
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3 Comments
 
LVL 18

Accepted Solution

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Priest04 earned 125 total points
ID: 22836041
You should never count on having correct resultt when dealing with double variables. Why your code is not displaying the last j value (which should be 1) is because it is slightly larger than 1

ex

1.0000000000252

This is why, when using doubles in loop, you need to do next




for (double i = 0; i <= 1.01; i += 0.1)
{
   Debug.WriteLine(i);
}
 
for (double j = 0; j <= 1.01; j += 0.05)
{
   Debug.WriteLine(j);
}

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LVL 18

Expert Comment

by:Priest04
ID: 22836056
Add watch to j varaible and see what its value is when it loops.
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LVL 18

Expert Comment

by:Priest04
ID: 22841635
May I ask why B? What was incomplete in my answer?
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