int loc = target.find(letter);
if (loc == string::npos)
{
cout << "Oh, bad guess!\n";
--guesses;
badchars += letter; // add to string
}
else
{
cout << "Good guess!\n";
attempt[loc]=letter;
// check if letter appears again
loc = target.find(letter, loc + 1);
while (loc != string::npos)
{
attempt[loc]=letter;
loc = target.find(letter, loc + 1);
}
}
cout << "Your word: " << attempt << endl;
if (attempt != target)
{
if (badchars.length() > 0)
cout << "Bad choices: " << badchars << endl;
cout << guesses << " bad guesses left\n";
}
}
if (guesses > 0)
cout << "That's right!\n";
else
cout << "Sorry, the word is " << target << ".\n";
cout << "Will you play another?
cin >> play;
play = tolower(play);
}
cout << "Bye\n";
return 0;
}
Here’s a sample run of the program in Listing 16.3:
Will you play a word game?
Guess my secret word. It has 6 letters, and you guess
one letter at a time. You get 6 wrong guesses.
Your word: ------
Guess a letter: e
Oh, bad guess!
Your word: ------
Bad choices: e
5 bad guesses left
Guess a letter: a
Good guess!
Your word: a--a--
Bad choices: e
5 bad guesses left
Guess a letter: t
Oh, bad guess!
Your word: a--a--
Bad choices: et
4 bad guesses left
Guess a letter: r
Good guess!
Your word: a--ar-
Bad choices: et
4 bad guesses left
Guess a letter: y
Good guess!
Your word: a--ary
Bad choices: et
4 bad guesses left
Guess a letter: i
Good guess!
Your word: a-iary
Bad choices: et
4 bad guesses left
Guess a letter: p
Good guess!
Your word: apiary
That's right!
Will you play another?
Bye
Program Notes
In Listing 16.3, the fact that the relational operators are overloaded lets you treat strings in the same fashion you would treat numeric variables:
while (guesses > 0 && attempt != target)
This is easier to follow than, say, using strcmp() with C-style strings.
The program uses find() to check whether a character was selected earlier; if it was already selected, it will be found in either the badchars string (bad guesses) or in the attempt string (good guesses):
if (badchars.find(letter) != string::npos
|| attempt.find(letter) != string::npos)
The npos variable is a static member of the string class. Its value, recall, is the maximum allowable number of characters for a string object. Therefore, because indexing begins at zero, it is one greater than the largest possible index and can be used to indicate failure to find a character or a string.
The program makes use of the fact that one of the overloaded versions of the += operator lets you append individual characters to a string:
badchars += letter; // append a char to a string object
The heart of the program begins by checking whether the chosen letter is in the mystery word:
int loc = target.find(letter);
If loc is a valid value, the letter can be placed in the corresponding location in the answer string:
attempt[loc]=letter;
However, a given letter might occur more than once in the mystery word, so the program has to keep checking. The program uses the optional second argument to find(), which specifies a starting place in the string from which to begin the search. Because the letter was found at location loc, the next search should begin at loc + 1. A while loop keeps the search going until no more occurrences of that character are found. Note that find() indicates failure if loc is after the end of the string:
// check if letter appears again
loc = target.find(letter, loc + 1);
while (loc != string::npos)
{
attempt[loc]=letter;
loc = target.find(letter, loc + 1);
}
What Else Does the string Class Offer?
The string library supplies many other facilities. There are functions for erasing part or all of a string, for replacing part or all of one string with part or all of another string, for inserting material into a string or removing material from a string, for comparing part or all of one string with part or all of another string, and for extracting a substring from a string. There’s a function for copying part of one string to another string, and there’s a function for swapping the contents of two strings. Most of these functions are overloaded so that they can work with C-style strings as well as with string objects. Appendix F describes the string library function briefly, but let’s talk about a few more features here.
