Infinite loop in while statement with cin

[lvinaja]

Why does this loop run infinitely?? Shouldn't it pause and allow me to make a new entry? Instead it just prints "How many players ....? - Error message 2" infinitely ... Obviously, I tried to use the uncommented ignore in case there was a return in the buffer, but that changes nothing ...

int counter=0;

while(counter<1 || counter>22)
{
//cin.ignore();

cout << "How many players are in the game (not counting the dealer)? - ";
cin >> counter;

if (!isdigit(counter))
counter=0;

if (counter>22)
cout << "Error message 1";
if (counter<1)
cout << "Error message 2";
}

Thanks -

Luc

[Protomega]

You never increment counter. Do this via counter++;

[lvinaja]

I think you are confused ... This is not a for loop, it is a while loop. As long as the user enters a number between 1-22 the loop will exit, and the program will continue. There is no need to increment as action is taken on what the user enters, not on a number of iterations ... Thanks though.

[lvinaja]

Really the program runs fine as long as a number is added, it is when a user enters an alpha that the infinite loop happens (sorry for not specifying that sooner).

[Protomega]

It's happening because a character will convert to 0, which means that counter is then less than 1 which will continuously put out Error message 2 because the parameters for your while loop keeps looking at the counter. You need to change the parameters for your while loop.

[lvinaja]

OK, in case anyone else runs across this problem ...

The while loop is fine obviously (it does what it should). The issue is in the isdigit/isalpha, which SHOULD return an int (0 or some other) and then you should be able to act on that. For some reason however, it seems to leave a return or 0 in the buffer (not just returning 0 to the point of use/analysis - my best guess) so you can never cin again to change the entry. Thus you need to:

char entry[80];
int counter=0;

while(counter<1 || counter>22)
{
cout << "How many players are in the game (not counting the dealer)? - ";
cin >> entry;

if (checkForInt(entry)==false)
cout << "That is not a valid entry." << endl;
else
counter = atoi(entry);


if (counter>22)
cout << "Error1" <<
"Please try again ...\n\n";
if (counter<1)
cout << "Error2" <<
"Please try again ...\n\n";
}

bool checkForInt(const char *str)
{
// is the string empty?
if (strlen(str) == 0)
return false;

//else
while (*str!='\0')
{
if (*str<'0' || *str>'9')
return false; // not a digit
str++;//move to next char
}

return true;//if all digits
}