c ++验证输入不起作用

Question

我在下面写了这段代码，一切正常，除非我输入多个字符时它假设给出无效输入而不退出程序但是当我写多个字符时会发生什么，从'Q'或'q'开始它退出程序，我不希望我只想在输入“q”或“Q”时退出

int main()
{
    char grade;

    while(grade!='Q'&& grade!='q') {

        cout<<"\nEnter one grade Letter from the following"
            <<" (A ,B,C,D or F) or Please or 'q' to quite: ";

        cin>>grade;
        if (cin.get() != '\n') // Look at the next character
            {

                cin.ignore(1000, '\n'); // Clear the input stream

                cout << "\nInvalid input !\n";
            }

        else if (grade != 'A' && grade != 'a'
                 &&  grade != 'B' && grade != 'b'
                 &&  grade != 'C' && grade != 'c'
                 &&  grade != 'D' && grade != 'd'
                 &&  grade != 'F' && grade != 'f'
                 &&  grade != 'Q' && grade != 'q'
                 ) {

            cout << "\nInvalid input !\n";

        }

        else if(grade =='A'||grade=='a')
            cout<<"Excellent"<<endl;
        else if(grade=='B'|| grade=='b')
            cout<<"Good"<<endl;
        else if(grade=='C' || grade=='c')
            cout<<"Fair"<<endl;
        else if (grade=='D' || grade=='d')
            cout<<"Poor"<<endl;
        else if (grade=='F' || grade=='f')
            cout<<"Failure"<<endl;
        //else

    }

    return 0;
}

Answer 1

如果您不想只考虑输入的第一个字符，则不要读取单个字符，然后根据它做出所有决定。 使用std::getline()将整行读入std::string ，然后检查它的有效值。

此外，您现有的代码具有未定义的行为，因为grade在首次使用之前未初始化。