Get number of digits of a number

Question

I have a number like this: int num = 36729; and I want to get the number of digits that compose the number (in this case 5 digits).

How can I do this?

Answer 1

1. The number of digits of an integer n in any base is trivially obtained by dividing until you're done:

unsigned int number_of_digits = 0;
do {
    ++number_of_digits; 
    n /= base;
} while (n);

2. Not necessarily the most efficient, but one of the shortest and most readable using C++: std::to_string(num).length()

3. And there is a much better way to do it:

#include<cmath>
...
int size = trunc(log10(num)) + 1
...

Answer 2

int digits = 0;
while (num > 0) {
  ++digits;
  num = num / 10;
}

Answer 3

int unsigned_digit_count(unsigned val) {
    int count = 0;
    do {
        count++;
        val /= 10;
    } while (val);
    return count;
}

int digit_count(int val) {
    if (val < 0) {
        return 1+unsigned_digit_count(-val); // extra digit for the '-'
    } else {
        return unsigned_digit_count(val);
    }
}