c++ - 如何忽略来自 std::cin 的非字母

Question

因此，我试图从 cin 中读取一个字符串，然后遍历该字符串以计算该字符串中哪些字符实际上是英文字母表中的字母。我编写了一个运行良好的程序，但我想知道是否有更有效的方法来执行此操作，而无需遍历整个英文字母表。

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

int main() {

    string my_str; //will use to store user input
    getline(cin, my_str); //read in user input to my_str

     int countOfLetters = 0; //begine count at 0
     string alphabet = "abcdefghijklmnopqrstuwxyz"; //the entire english alphabet

     for(int i = 0; i < my_str.length(); i++){
        for(int j = 0; j < alphabet.length(); j++){
            if (tolower(my_str.at(i)) == alphabet.at(j)){ //tolower() function used to convert all characters from user inputted string to lower case
                    countOfLetters += 1;
            }
        }
     }

     cout << countOfLetters;
    return 0;
}

编辑:这是我改进后的新代码:

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

int main() {

    string my_str; //will use to store user input
    getline(cin, my_str); //read in user input to my_str

     int countOfLetters = 0; //begine count at 0
     string alphabet = "abcdefghijklmnopqrstuwxyz"; //the entire english alphabet

     for(unsigned int i = 0; i < my_str.length(); i++){
            if (isalpha(my_str.at(i))){ //tolower() function used to convert all characters from user inputted string to lower case
                    countOfLetters += 1;
            }
        }


     cout << countOfLetters;
    return 0;
}
    enter code here

Answer 1

使用isalpha()查看哪些字符是字母并排除它们。

因此，您可以像这样修改您的代码:

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

int main() {

  string my_str;
  getline(cin, my_str);

  int countOfLetters = 0;

  for (size_t i = 0; i < my_str.length(); i++) { // int i produced a warning
    if (isalpha(my_str.at(i))) {  // if current character is letter
      ++countOfLetters;           // increase counter by one
    }
  }

  cout << countOfLetters;
  return 0;
}