基於字符串長度的測驗函數中的錯誤

Question

我在這個基本的C++測驗程序中遇到了一些小麻煩。在主函數中，我讓用戶輸入他/她的名字，並將該字符串傳遞給下一個函數take_quiz。但是，我注意到如果我在其中包含一個名稱（如名和姓），會發生錯誤。出於某種原因，第二個單詞中的字母數量會產生相同數量的「請輸入有效答案（a，b，c，d）」。我認爲這很奇怪，因爲只有在take_quiz中的變量的第一個cin後面使用內聯函數valCheck時纔會發生提示。我需要一些幫助來確定問題並予以糾正。謝謝！

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

得到的字符串輸入您的valCheck()不返回任何東西 - 根據簽名，它需要返回一個char值。如果您的字符串包含換行符，則您希望使用std::getline(std::cin, str);而不是std::cin。 std::cin默認會跳過空格。此外，您之前未調用原型函數即可調用take_quiz()，因此您需要將其移至main()以上或至少在上面指定函數簽名。

完整的程序應該是這樣的（如果quiz_results[0]等於'b'，您只需要添加一個檢查）。

#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

我改如何從用戶

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; 
    }