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Registered Member #1845
Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211
Suppose a block of code asks a user to enter a y or n, and then I want to check if the user just hits enter. If I declare a variable char to hold the value, can I check if they just simply hit enter, instead of entering the y or n. This is easily done if I declare a string to hold the y or n. I just check for an empty string, (like "") but I get an error if I check for a '' (like an empty character) I asked this question to a professional programmer yesterday, and he said it wasn't possible to check for the empty character, at least the way I have proposed, but really? Why?
//Code that works
cout << "Enter a y or n "; string letter; getline(cin,letter); //assume user just hits enter and doesn't type a letter
if (letter == "") { cout << "Hey, you didn't enter a letter"; }
//Code that doesn't work, it issues and empty character constant error, or some crap like that
cout << "Enter a y or n "; char letter; cin >> letter; //assume user just hits enter and doesn't type a letter
if (letter == '') { cout << "Hey, you didn't enter a letter"; }
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
A string can contain any reasonable number of characters including zero characters, that is why the first program works.
A char is really an integer, it can hold a any number within a certain range. That range does not contain "not a number". So you can't store "not a number" in a char.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Doing this kind of thing in C/C++ is difficult and annoying. When you use << to get input, I guess it returns nothing if you just press enter. But << should only be used with a C++ string, not a char.
Also as Bjorn points out, a C++ string can have the property of "emptiness" but a char can't. The closest thing a char could be is NULL, but even that is a valid ASCII character, so it's still not "empty". That's why the professional programmer said that it can't be done.
Below I showed code that would give you the result "y" or "n" in a char. But you probably should stick with C++ "string"s throughout, they behave more like the kids of today expect strings to behave in VB, PHP and so on.
//Here's how I would kludge it. I haven't tested it though. Watch out for Unicode problems on Windows.
cout << "Enter a y or n ";
string letter;
char checked_letter;
getline(cin,letter); //assume user just hits enter and doesn't type a letter
if (letter == "")
{
cout << "Hey, you didn't enter a letter";
checked_letter = NULL;
}
else
{
// Convert C++ string to regular one and take first character
checked_letter = letter.c_str()[0];
}
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C++ question
