im new to C++ and i got an assignment which required me to do a
hangman game. Global variables are not allowed. program must be
modular, i.e create suitable functions. for functions, i was told to
use reference parameters instead of pointer parameters. i am to use
string class and not character array(e.g char x[20]).whenever
possible, you are to use keyword 'const' for function parameters and
prototype.

1. write a program (guess.cpp) that allows user to play the Hangman
game, as follows:

a) program 1st prompts user to enter a number between 1 - 20, reads a
word to guess from a file guess.txt, based on the number entered. the
file has the following format:

word1 PrizeAmount
word2 PrizeAmount
word3 PrizeAmount
:
:
:
word20 PrizeAmount

b) program then prompts the user to guess a letter. if the letter is
in the word, that letter will be displayed in the position(s) it
occurs. if it is incorrect, the incorrect letter is added to the
string of incorrect guesses and the number of attempts is incremented
by 1.

c) if user guesses a letter which he/she already guessed before,
program should display an error message and it should not increase the
number of attempts.

d) the user wins if he/she guesses the word with no more than 7
incorrect guesses. if user wins, the prize amount is added to his
earnings (initially set to $0). if user loses, the prize amount is
deducted from his earnings and program wil display the word to guess.

e) program will quit if user's earnings is less than $0 or he chooses
to quit the game after each round.

f) as an illustration, suppose the file guess.txt has the following
content:
life 50
home 100
house 150

if user enters a number 3, the word to guess will be "house".