infinite loop due to buffer value -1? - c++

Question

I'm writing this program for class. It's supposed to take in a word 10 or less chars in size and change each char individually to uppercase using a toupper() call. The requirements of the assignment are to use toupper() on each individual char in an array that holds the word and the '\n'. Here is my code:
int main(int argc, char *argv[])
{
char again = ' ';
char word[11];
for(int count=0; count<11; count++){
word[count] = ' ';
}
while(true){
for(int clear=0; clear < 11; clear++){
word[clear] = ' ';
}
system("CLS");
cout << "Please provide a lowercase word!" << endl;
cin.getline(word, 11);
for(int letter = 0; letter < 11; letter++){
system("CLS");
if(letter < 10){
word[letter] = toupper(word[letter]);
}
for(int printw = 0; printw < 11; printw++){
cout << word[printw];
}
Sleep(200);
}
cout << endl;
while(true){
cout << "Would you like to Repeat or Quit? (R/Q)" << endl;
cin.get(again);
cin.get();
tolower(again);
if(again == 'r' || again == 'q'){
break;
}
else{
cout << "That was an invalide input!" << endl;
}
}
if(again == 'q'){
break;
}
}
system("PAUSE");
return EXIT_SUCCESS;
}
The program works just fine for 1 - 10 char words, but if the user decides to enter a string larger than 10 chars, the program will uppercase the first 10 and then hit an infinite loop when it asks if the user would like to try again. When that happens it will continue to return "That was an invalid output!" and the next prompt to repeat or quit on the next line. It will not wait for input, and I've tried clearing the buffer with cin.ignore().
I tried checking the values in the buffer with several cout << cin.get() << endl; line and they all come back with the ascii value of -1. I assume this means it is throwing a failbit exception, but I'm not actually sure.

Answer 1

Instead of using a character array of fixed size, you should use a string to store your input. You can use getline to read a line from cin like this:
string input;
...
getline(cin, input);
This will read the entire line, regardless of how long it is or how many characters you actually process.

Answer 2

What you're seeing here is the expected behaviour of cin.getline(char* s, streamsize n) From C++ ref for istream::getline:
The failbit flag is set if the function extracts no characters, or if
the delimiting character is not found once (n-1) characters have
already been written to s.
If a user types a word longer than 10 chars, then cin writes the first 10 chars to word and sets its internal flag to fail as no delimiter \n (newline) has been seen.
If you want to stick to your current solution, you could overcome this with:
const int SIZE = 11;
...
cin.getline(word, SIZE);
if (cin.fail() && cin.gcount() == SIZE-1) { // failed because user entered a word longer than 10 chars
word[SIZE-1] = '\0'; // make sure to null terminate
cin.clear(); // clear the failure from cin
cin.ignore(256, '\n'); // ignore the leftover input from cin until next newline
}
You need to both clear the failbit and ignore the leftover input. 256 is simply a number large enough, to be super safe you can use cin.ignore(numeric_limits<streamsize>::max(), '\n'); (don't forget to #include <limits>)
PS You might be better off reading a char at a time with cin.get(char& c) though.