How to know the number of digits in an integer - c++

Question

I'm new to programming, and I'm wondering, how can I know the number of digits in an integer that the user enters? For example: the user enters a number like 123456, how can I know that the user enters 6 digits? I don't want to use a for loop to get user input because I don't want the user to enter each digit after a space or enter.
Right now, I'm converting a number to an array of digits so I can have control over them, but the issue is that I don't know how many digits I should loop over, because I don't know how many digits are in the number.
Can I get the user's input as a string and then use string.length and convert it to an array of digits?
#include <iostream>
using namespace std;
int main()
{
int N;
cin >> N;
while(N--)
{
int num;
cin >> num;
int arr[1000];
for (int i=0 ;i<???;i++)
{
arr.[i]=num%10;
num = num /10;
}
}
}

Answer 1

an easier way to do this is to convert it to a string then count the length of said string
#include <iostream>
#include <string>
using namespace std;
int main() {
int n;
cin >> n;
string str = to_string(n);
cout <<"the length of" <<str << "is:" <<str.length() <<"\n";
}
typing in a 41 will print out.
the length of 41 is 2

Answer 2

while (num != 0)
{
arr.[i]=num%10;
num = num /10;
}
is a common pattern that's close to what you already have.
Although you can do what you mentioned in your question and someone suggested in the comments and get the input as a string and use string.length.

Answer 3

Yes, you can read in the user's input as a std::string instead of as an int, and then you can use std::string::size() (or std::string::length()) to get the number of characters in the string, eg:
#include <iostream>
#include <string>
int main()
{
std::string S;
std::cin >> S;
int arr[1000] = {};
for (size_t i = 0; i < S.size(); ++i)
{
arr[i] = (S[i] - '0');
}
return 0;
}
Alternatively:
#include <iostream>
#include <string>
#include <algorithm>
int main()
{
std::string S;
std::cin >> S;
int arr[1000] = {};
std::transform(S.begin(), S.end(), arr, [](char ch){ return int(ch - '0'); });
return 0;
}
Either way, if needed, you can check if the std::string represents a valid integer using std::stoi() or std::strtol() or other similar function, or by putting the std::string into a std::istringstream and then reading an integer from it.
Otherwise, you can read the user's input as an int and then convert it to a std::string for processing:
#include <iostream>
#include <string>
int main()
{
unsigned int N;
std::cin >> N;
std::string S = std::to_string(N);
int arr[1000] = {};
for (size_t i = 0; i < S.size(); ++i)
{
arr[i] = (S[i] - '0');
}
// or:
// std::transform(S.begin(), S.end(), arr, [](char ch){ return int(ch - '0'); });
return 0;
}
Otherwise, if you really want to read in an int and loop through its digits directly, you can use something more like this:
#include <iostream>
int main()
{
unsigned int N;
std::cin >> N;
int arr[1000] = {};
size_t i = 0;
while (N != 0)
{
arr[i++] = num % 10;
num /= 10;
}
return 0;
}