#!/usr/bin/perl

print "Please, what is 2+2?  You can answer\n";
print "   a number to guess\n";
print "   ? to ask me again what the question is,\n";
print "   R to retry,\n";
print "or Q to quit or A to abort.\n";

# Note that while (<>) {       is not quite the same as
#       the while (<STDIN>) {  I have below.
#
# A bare (<>) means to read from the argument list (ARGV) first,
# or if it's empty, then and only then, read from STDIN.
while (<STDIN>) {
  chomp;
  $answer=$_;
  # print "Checking >$answer<\n";

  if ($answer) {                 # Catch null answer
    if ($answer =~ /^\d+$/) {    # Numeric answer?
      if ($answer==4) {
        print "\nYeah!  You finally got it right.  2+2 = $answer.\n";
        exit;
      } else {
        print "Good try, but wrong.  2+2 is not $answer.  Try again.\n";
      }
    } elsif ($answer=~/^a(bort)?$/i || $answer=~/^q(uit)?$/i) {                 
      print "Giving up, huh.  Ok, bye.\n";
      last;
    } elsif ($answer=~/^r(etry)?$/i) {                 
      print "I said, what's 2+2?\n";
    } else {
      print "Invalid response ($answer).\n";
    }
  } else {
    # print "Empty answer detected.\n";
  }
}