EDIT2: cut all this, but basically, when you learn arrays, this will be so much easier.
EDIT: unrelated to the problem, but don't the conditions in your else
block need to occur regardless of whether the guess was successful or not? You increment the count in both instances, and you'll need to blank out the guessed character whether it existed or not, correct?
PSUEDOCODE for inside the "successful guess":
String temporaryGuess = "";
for-loop for each character in originalString {
if (character at current index = guess)
append guess to temporaryGuess;
else
append a ? to temporaryGuess;
}
set the previous guessed String to the temporaryGuess String