2. C++ 统计字符串中英文字母、空格、数字和其它字符的个数

输入一行字符，分别统计其中字母、空格、数字和其他字符的个数。
 1 //
 2 // Created by Green on 2021/6/9.
 3 //
 4 #include <iostream>
 5 
 6 using namespace std;
 7 int letters, digit, space, others;
 8 
 9 int main(void) {
10     cout << "please input some characters" << endl;
11     int c;
12     while ((c = getchar()) != ‘\n‘) {
13         if (c >= ‘a‘ && c <= ‘z‘ || c >= ‘A‘ && c <= ‘Z‘) {
14             letters++;
15         } else if (c == 32) {
16             space++;
17         } else if (c >= ‘0‘ && c <= ‘9‘) {
18             digit++;
19         } else {
20             others++;
21         }
22     }
23     cout << "letters: " << letters << endl
24          << "digit: " << digit << endl
25          << "space: " << space << endl
26          << "others: " << others << endl;
27     return 0;
28 }