3. 输入一个正整数求出它是几位数：输出原数和位数。

#include <iostream>
#include <string>

using namespace std;
int digit;

int main(void) {
    void count(string str);
    printf("Please input numbers:\n");
    string text;
    cin >> text;
    count(text);
    cout << "原数: " << text << endl;
    cout << "位数" << digit << endl;
    return 0;
}

void count(string str) {
    int i;
    for (i = 0; str[i] != '\0'; i++) {
        if (str[i] >= '0' && str[i] <= '9') {
            digit++;
        }
    }
}