c++ - 接受用户输入时的错误处理第 2 部分

Question

我之前提过一个问题: error handling when taking user input

然后我进行了建议的更改:

char displayMainMenu()
{
char mainMenuChoice;
cout << "\nQuadratic equation: a*X^2 + b*X + c = 0 main menu: "; 
cout << "\n <r>  Give new coefficients"; 
cout << "\n <c>  Calculate equations solutions"; 
cout << "\n <t>  Terminate the program";
cout<<"Enter choice : ";
cin>>mainMenuChoice;
return mainMenuChoice;
}

int main()
{
bool done = false;
while(!done)
{
    char choice = displayMainMenu();  
    switch(tolower(choice))
    {
        case 'r':
                cout<<"Entered case 'r'";
                break;
        case 'c':
                cout<<"Entered case 'c'";
                break;  
        case 't':
                cout<<"Entered case 't'";                   
                break;
        default:
                cout<<"Invalid choice! Try again"<<endl;   
    }
}
return 0;
}

新的问题是，如果用户输入错误，让我们说“ter”，我会得到以下信息 :( :

Quadratic equation: a*X^2 + b*X + c = 0 main menu:   
 <r>  Give new coefficients 
 <c>  Calculate equations solutions  
 <t>  Terminate the program 
Enter choice : ter 
Entered case 't'

Quadratic equation: a*X^2 + b*X + c = 0 main menu:  
 <r>  Give new coefficients 
 <c>  Calculate equations solutions  
 <t>  Terminate the program 
Enter choice : Invalid choice! Try again

Quadratic equation: a*X^2 + b*X + c = 0 main menu:  
 <r>  Give new coefficients 
 <c>  Calculate equations solutions  
 <t>  Terminate the program 
Enter choice : Invalid choice! Try again

我怎样才能避免这种情况发生？

Answer 1

在您的 displayMainMenu() 函数中，不是读取 char，而是读取字符串。丢弃(警告)任何长度超过一个字符的输入。

你可以使用

char str[101]
std::cin.getline(str, 101);

代替

cin >> mainMenuChoice;

为了读取字符串。