How to count amount of digits in a given number in c++

Question

Count amount of digits in a given number or input by the user.

Please be more specific about what you mean. If you ask a vague question people are unlikely to answer it. — templatetypedef, Jan 07 '11 at 10:20
http://stackoverflow.com/questions/554521/how-can-i-count-the-digits-in-an-integer-without-a-string-cast — Lukáš Lalinský, Jan 07 '11 at 10:22
Hint (assuming this is homework) - divide the number by ten until you hit zero. — Amarghosh, Jan 07 '11 at 10:35

Jakob · Accepted Answer · 2011-01-07T10:27:45.990

8

Independent of programming language:

floor(log10(x))+1

where x is your number (>0).

If you want to handle 0 and negative numbers, I'd suggest something like this:

x == 0 ? 1 : floor(log10(abs(x)))+1

edited Jan 07 '11 at 10:27

answered Jan 07 '11 at 10:21

Jakob

If `x==0` guard with an `if`, it's probably the best way to handle this, and put abs(x) inside the log to handle negatives, for which `log10` is undefined. – Jan 07 '11 at 10:24
@cHao: That's a tricky question. How many digits are there in the float `float x = 1.0/3`? Not very useful either. If the OP is actually asking about non-integers, I'd surrender to the obvious: treating the user input as a string and checking its length (minus characters that we don't care about). – Jakob Jan 07 '11 at 10:33
As for usefulness...yeah, it'd be kinda rare. However, there'd be uses, mostly when doing formatted text output and such. – cHao Jan 07 '11 at 10:40

score 4 · Answer 2 · answered Jan 07 '11 at 10:21

4

Convert the number to a string and count the characters.

answered Jan 07 '11 at 10:21

Karlth

score 0 · Answer 3 · answered Jan 07 '11 at 10:25

0

I assume you want to know how many base 10 digits do you need to represent a binary number (such as an int).

double x = something(positive); 
double base = 10.0; 
double digits = ceil(log(x + 1.0) / log(base));

answered Jan 07 '11 at 10:25

diego

3 Answers3