#!/usr/bin/perl
#<<mathq>>=
use warnings;
use strict;

print "Welcome to the math program\n";
my $quit = 0;
until ($quit) {
    my @numbers = gen_numbers();
    my ($question, $solution) = gen_question(@numbers);
    my $response = get_valid_response($question);
	
    #<<test response and display right or wrong>>=
    if ($response eq 'q') {
	$quit = 1; # set loop control to indicate the user has quit
    } elsif ($response = $solution) {
	print "Correct\n";
    } else {
	print "Incorrect: $question $solution\n";
    }
}
print "exiting the math program\n";

###### Subroutines

# gen_numbers: generate equation numbers (and operator)
# parameters: none
# returns: first_number, second_number, operator

sub gen_numbers {
    my $first_number  = int(rand(10)); # random integer from 0 to 9
    my $second_number = int(rand(10)); # random integer from 0 to 9
    # choose random operator code: 0 is division, 1 is multiplication
    my $operator  = int(rand(2)); # random integer from 0 to 1
    return ($first_number, $second_number, $operator);
}

# gen_question: <<generate a question and its solution>>=
# parameters:
#   first_number  (integer 0-9)
#   second_number (integer 0-9)
#   operator      (0 => division, 1 => multiplication)
# returns: question, solution

sub gen_question {
    my ($first_number, $second_number, $operator) = @_;
    my $solution;
    my $question;

    if ($operator == 1) {
        #<<create multiplication question and solution>>=
	$solution = $first_number * $second_number;
	$question = "$first_number x $second_number = ?";
    } else {
	#<<create division question and solution>>=
	$solution = $first_number * $second_number;
        # swap values of solution and first_number
	($solution, $first_number) = ($first_number, $solution);
	$question = "$first_number / $second_number = ?";
    }
    return ($question, $solution);
}

# get_valid_response: <<display question and get a valid response>>=
# parameters: question (string)
# returns: response

sub get_valid_response {
    my $question = $_[0];
    my $response;
    my $is_valid = 0;
    until ($is_valid) {
	print "$question\n";
	$response = <STDIN>;
	chomp($response);
	#<<test if input is valid>>=
	if ($response eq 'q' or $response =~ m/^\d+$/) {
	    $is_valid = 1;
	} else {
	    print "Invalid input: enter an integer or 'q' to quit\n";
	}
    }
    return $response;
}