C++ count the number of digits of a double

Question

i want to do what the title says like this:

int number1;
cin>>number1;
num1len=log10(number1)+1;
cout<<"num of digits is "<<num1len<<"\n";

but when the number of digits is 11 and more the answer is always 7(6+1)

Does anyone knows why or what im i doing wrong?

Answer 1

What is 'wrong' is the maximum value which can be stored in a (signed) int :

#include <iostream>
#include <numeric>

int main()
{
    std::cout << std::numeric_limits<int>::max() << std::endl;
}

Gives me :

2147483647