3. 輸入一個正整數求出它是幾位數：輸出原數和位數。

#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 << "原數: " << text << endl;
    cout << "位數" << 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++;
        }
    }
}