C++: how can I test if a number is power of ten?

Question

I want to test if a number double x is an integer power of 10. I could perhaps use cmath\'s log10 and then test if x == (int) x?

<

Answer 1

if you don't need it to be fast, use recursion. Pseudocode:

bool checkifpoweroften(double Candidadte)
     if Candidate>=10
         return (checkifpoweroften(Candidadte/10) 
     elsif Candidate<=0.1
         return (checkifpoweroften(Candidadte*10)
     elsif Candidate == 1
         return 1
     else 
         return 0

You still need to choose between false positives and false negatives and add tolerances accordingly, as other answers pointed out. The tolerances should apply to all comparisons, or else, for exemple, 9.99999999 would fail the >=10 comparison.