新手可用：

#include <bits/stdc++.h>
using namespace std;
int main() {
int x;
    cin >> x;
    int cnt = 0;
    if (x == 0)
        cnt = 1;
    else
    {
        while (x != 0)
        {
            x /= 10;
            cnt++;
        }
    }
    cout << cnt << endl;
    return 0;
}

老手用字符串：

#include <iostream>
#include <string>
using namespace std;

int main()
{
    string s;
    cin >> s;
    cout << s.size() << endl;
    return 0;
}