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algorithmfloating-pointpseudocodefloating-accuracy

Potential issue with floating point rounding

I was given the below problem and I want to make sure I fully understand before submitting it.

Explain briefly the problem that might arise if the following algorithm is implemented. (Hint: remember the problem of rounding error with floating point numbers) 

assign n the value 0.1 
while (n is not equal to 1.0) 
   print the value of n 
   assign n the value n + 0.00001
end while

I believe the answer is that is does not say what to do if the value of n is equal to 1.0. Am I looking at this right or am I missing something obvious?

Solution

  • The problem is that 0.00001 is not exactly representable in standard floating point so when you keep adding you will reach a number like 0.999999999998 instead of 1.0.

    Therefore n will never be equal to 1.0

    Therefore the loop will never terminate.