基于字符串长度的测验函数错误

Question

我在使用这个基本的 C++ 测验程序时遇到了一些小问题。在主函数中，我让用户输入他/她的姓名，然后将此字符串传递给下一个函数 take_quiz。但是，我注意到如果我包含一个带有空格的名称（如名字和姓氏），则会发生错误。出于某种原因，第二个单词中的字母数量会产生相同数量的“请输入有效答案（a、b、c、d）”的显示。我认为这很奇怪，因为该提示只能在使用内联函数 valCheck 时出现，该函数位于 take_quiz 中变量的第一个 cin 之后。我需要一些帮助来识别问题并纠正它。谢谢！

inline char valCheck(char& input)
    {
         tolower(input);
         while(input < 97 || input > 100)
         {    
             cout << "Please enter a valid answer (a, b, c, d):" << endl;
             cin  >> input;
         }
    }
    int main(int argc, char *argv[])
    {
         string name;

         cout << "This program will quiz your knowledge of C++. Please enter your name:" << endl;
         cin  >> name;
         cout << "Hello " << name << "! IT'S QUIZ TIME!!!" << endl;
         take_quiz(name);

         system("PAUSE");
         return EXIT_SUCCESS;
    }

    void take_quiz(string name2)
    {    
         char quiz_results[10];
         system("PAUSE");
         cout << "\nThe quiz will now begin.\nThis quiz covers topics such as data types, arrays, pointers, etc." << endl
              << "To answer the multiple choice questions,\nsimply input a, b, c, or d according to the given options." << endl
              << "The test will continue regardless if you enter a question wrong or right." << endl
              << "Good luck " << name2 << "!" << endl;
         system("PAUSE");
         cout << "\n1. What preprocessor command must one include to use the cout and cin function?" << endl
              << "\na.  #include <iomanip>" << endl
              << "b.    #include <iostream>" << endl
              << "c.    #include <cmath>" << endl
              << "d.    using namespace std;" << endl;
         cin >> quiz_results[0];
         valCheck(quiz_results[0]);

Answer 1

您的 valCheck() 不返回任何内容 - 根据签名，它需要返回一个 char 值。如果您的字符串包含换行符，您想使用std::getline(std::cin, str); 而不是std::cin。 std::cin 默认会跳过空格。此外，您之前在没有原型函数的情况下调用 take_quiz()，因此您需要将其移至 main() 上方或至少在上方指定函数签名。

完整的程序应该是这样的（你只需要添加一个检查quiz_results[0]是否等于'b'）。

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

inline char valCheck(char& input){
  tolower(input);
  while (input < 97 || input > 100){
    cout << "Please enter a valid answer (a, b, c, d):" << endl;
    cin >> input;
  }
  return input;
}
void take_quiz(string name2)
{
  char quiz_results[10];
  system("PAUSE");
  cout << "\nThe quiz will now begin.\nThis quiz covers topics such as data types, arrays, pointers, etc." << endl
    << "To answer the multiple choice questions,\nsimply input a, b, c, or d according to the given options." << endl
    << "The test will continue regardless if you enter a question wrong or right." << endl
    << "Good luck " << name2 << "!" << endl;
  system("PAUSE");
  cout << "\n1. What preprocessor command must one include to use the cout and cin function?" << endl
    << "\na.  #include <iomanip>" << endl
    << "b.  #include <iostream>" << endl
    << "c.  #include <cmath>" << endl
    << "d.  using namespace std;" << endl;
  cin >> quiz_results[0];
  valCheck(quiz_results[0]);
}

int main(int argc, char *argv[]){
  string name;
  cout << "This program will quiz your knowledge of C++. Please enter your name:" << endl;
  std::getline(std::cin, name);
  cout << "Hello " << name << "! IT'S QUIZ TIME!!!" << endl;
  take_quiz(name);
  system("PAUSE");
  return EXIT_SUCCESS;
}

Answer 2

我更改了如何从用户获取字符串输入

    int main(int argc, char *argv[])
    {
         char name[100];
         cout << "This program will quiz your knowledge of C++. Please enter  your name:" << endl;
         cin.getline(name,sizeof(name));
         //cin  >> name;
         cout << "Hello " << name << "! IT'S QUIZ TIME!!!" << endl;
         take_quiz(name);

         system("PAUSE");
         return EXIT_SUCCESS;
    }