#!/usr/bin/perl -w

use strict;

#
# Use uppercase for the city names to make it easier to compare the
# user's answers.  For the country names, it just makes it easier for
# the user to find the relevant part of the question.
#
my %capitals = ("UNITED STATES OF AMERICA" => "WASHINGTON",
                "RUSSIA"                   => "MOSCOW",
                "INDIA"                    => "NEW DELHI",
                "CHINA"                    => "BEIJING");

my @countries = keys %capitals;

#
# We start off with $asked set to -1 because when they type 'QUIT' it
# will be one higher than we would like, since that question should
# not be counted.
#
# I am setting $answer to "" because as of the time when this was
# assigned, "last" had not yet been taught.  A better way to do this
# is to use an infinite loop ("while(1)") and use "last" when they
# type "QUIT".  This way, the test for "QUIT" would not need to appear
# more than once.  Think what might happen if the exit command was
# changed from "QUIT" to "EXIT"?  You would have to modify two places,
# and if you didn't notice that you might cause a bug.
#
my $answer  = "";
my $asked   = -1;
my $correct = 0;

while(uc $answer ne 'QUIT')
{
    #
    # Since rand(4) generates a number between 0 and 3.999999..., using
    # int() makes it in the range 0 to 3, inclusive.
    #
    my $i = int(rand(@countries));

    #
    # Ask the question
    #
    my $country = $countries[$i];
    print "What is the capital of $country? ";
    chomp($answer = <STDIN>);
    $asked++;

    #
    # Check the answer
    #
    if (uc $answer eq $capitals{$country})
    {
        print "That is correct!\n";
        $correct++;
    }
    elsif (uc $answer ne 'QUIT')
    {
        print "Sorry, that is incorrect.\n";
    }
}

#
# Compute and display score.
#
my $pct = int($correct * 100 / $asked);
print("Thank you for playing!  ",
      "You got $correct out of $asked right ($pct%).\n");