Bizarre cin.get() problems (I suspect)

[foahchon]

Hi, I'm trying to write a simple program (or portion of a program), that will re-prompt a user for input each time the user enters invalid input, and then exit once the user has entered valid input. Here's what I have so far in main():

int main()
{
char input[SIZE];

cout << "Enter a string: ";

while (!InputString(input))
{
cout << "Invalid string entered. Try again: " << endl;
}

system("pause");
return 0;
}

And here's the body of the InputString() function:

bool InputString(char str[SIZE])
{
char ch;
int x = 0;

while ((ch = cin.get()) != '\n')
{
if (x != (SIZE - 1))
{
str[x++] = ch;
}
else
{
str[x] = '\0';
return false;
}
}

str[x] = '\0';

return true;
}

The odd thing that ends up happening is, "Invalid string entered. Try again: " is displayed three times, and then the program exits as if valid input was entered. Anyone know what's going wrong? Thanks.

[horace1]

what is the value of SIZE ? the program will work OK so long as less than SIZE characters are entered on a line. If more are entered it will keep reading the rest of the input stream until it finds less than SIZE characters on a line. Try using cin.ignore() to remove any characters on a line if input fails, e.g. also added a statement to print input if it is OK

int main()
{
char input[SIZE];
 
cout << "Enter a string: ";
 
while (!InputString(input))
{
cout << "Invalid string entered. Try again: " << endl;
cin.ignore(1000,'\n');  // ignore rest of characters on the line
}
cout << "input " << input << endl;
system("pause");
return 0;
}
 

[foahchon]

Thanks a lot for your reply. I figured I might have to use cin.ignore(), I just wasn't sure where or how. The value of the SIZE constant is 101. The maximum number of characters allowed in order for a string to be valid is 100, plus a terminating null character. Should I use the SIZE constant in the cin.ignore() call, instead of 1000, which seems to be generic?

[horace1]

[quote=horace1]ignore() extracts and discard characters

cin.ignore(int length, char t = EOF)
 

Extracts and discards up to length characters from cin or until the termination character t or EOF is found (the termination character is extracted).

I usually just put a large number for length (to make sure all excess characters are removed) but the recommended way is

  cin.ignore(numeric_limits<int>::max(), '\n');
 

where numeric_limits<int>::max() returns the maximum finite value of an int and the termination character is newline