algorithm - Get number of digits in an unsigned long integer c# -

i'm trying determine number of digits in c# ulong number, i'm trying using math logic rather using tostring().length. have not benchmarked 2 approaches have seen other posts using system.math.floor(system.math.log10(number)) + 1 determine number of digits. seems work fine until transition 999999999999997 999999999999998 @ point, start getting incorrect count.

has encountered issue before ?

i have seen similar posts java emphasis @ why log(1000)/log(10) isn't same log10(1000)? , post @ how separate digits of int number? indicates how possibly achieve same using % operator lot more code

here code used simulate this

action<ulong> displayinfo = number =>   console.writeline("{0,-20} {1,-20} {2,-20} {3,-20} {4,-20}",    number,    number.tostring().length,    system.math.log10(number),    system.math.floor(system.math.log10(number)),   system.math.floor(system.math.log10(number)) + 1);  array.foreach(new ulong[] {  9u,  99u,  999u,  9999u,  99999u,  999999u,  9999999u,  99999999u,  999999999u,  9999999999u,  99999999999u,  999999999999u,  9999999999999u,  99999999999999u,  999999999999999u,  9999999999999999u,  99999999999999999u,  999999999999999999u,  9999999999999999999u}, displayinfo);  array.foreach(new ulong[] {  1u,  19u,  199u,  1999u,  19999u,  199999u,  1999999u,  19999999u,  199999999u,  1999999999u,  19999999999u,  199999999999u,  1999999999999u,  19999999999999u,  199999999999999u,  1999999999999999u,  19999999999999999u,  199999999999999999u,  1999999999999999999u }, displayinfo); 

thanks in advance

pat

log10 going involve floating point conversion - hence rounding error. error pretty small double, big deal exact integer!

excluding .tostring() method , floating point method, yes think going have use iterative method use integer divide rather modulo.

integer divide 10. result>0? if iterate around. if not, stop. number of digits number of iterations required.

eg. 5 -> 0; 1 iteration = 1 digit.

1234 -> 123 -> 12 -> 1 -> 0; 4 iterations = 4 digits.