c++ validate input does not work

Question

I am writing this code below and everything is working fine except when I type multiple characterS it suppose to give invalid input without exit the program but what is happen that when I wrote multiple characters starting quite 'Q' or 'q' it is exit the program and I do not want that I only want to exit if I type 'q' or 'Q'

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

If you do not want to take into consideration only the first character that's entered, then don't read a single character and then base all the decisions on it. Use std::getline() to read an entire line into a std::string , and then check it for valid values.

Additionally, your existing code has undefined behavior, because grade is uninitialized before its first use.