C/C++ counting the number of decimals?

Question

Lets say that input from the user is a decimal number, ex. 5.2155 (having 4 decimal digits). It can be stored freely (int,double) etc.

Is there any

Answer 1

This is a robust C++ 11 implementation suitable for float and double types:

#include 
#include 
#include 

template 
std::enable_if_t<(std::is_floating_point::value), std::size_t>
decimal_places(T v)
{
    std::size_t count = 0;

    v = std::abs(v);

    auto c = v - std::floor(v);

    T factor = 10;

    while (c > 0 && count < std::numeric_limits::max_digits10)
    {
        c = v * factor;

        c = c - std::floor(c);

        factor *= 10;

        count++;
    }

    return count;
}

It throws the value away each iteration and instead keeps track of a power of 10 multiplier to avoid rounding issues building up.