3. 输入一个正整数求出它是几位数：输出原数和位数。

 1 #include <iostream>
 2 #include <string>
 3 
 4 using namespace std;
 5 int digit;
 6 
 7 int main(void) {
 8     void count(string str);
 9     printf("Please input numbers:
");
10     string text;
11     cin >> text;
12     count(text);
13     cout << "原数: " << text << endl;
14     cout << "位数" << digit << endl;
15     return 0;
16 }
17 
18 void count(string str) {
19     int i;
20     for (i = 0; str[i] != ''; i++) {
21         if (str[i] >= '0' && str[i] <= '9') {
22             digit++;
23         }
24     }
25 }