Question

I’m very new to Perl and have been given an assignment that is a simple guessing game where the user is given 8 chances to guess a number between 1 and 100. I keep getting the error mentioned above and cannot figure it out.

Here’s my code:

    use Modern::Perl;

    my ($guess,$target,$counter); 
    $target = (int rand 100) + 1;

    while ($guess < $target)
    {
        chomp ($guess=<>);
        print "Enter guess $counter: ";

        $counter++;

        if ($guess eq $target) {
            print "\nCongratulations! You guessed the secret number $target in   $counter";
        }
        elsif ($guess > $target) {
            print "\nYour guess, $guess, is too high.";
        }
        elsif ($guess < $target) {
            print "\nYour guess, $guess, is too low.";
        }
        else {
            print "You lose. The number was $target.";
        }
    }

Answer 1

Your code suffers a few issues. Here is my code, using a different approach:

#!/usr/bin/perl

use 5.012;   # use strict; use feature 'say';
use warnings;

my $number = (int rand 100) + 1;
my $max_guesses = 8;

GUESS: foreach my $guess_no (1..$max_guesses) {
  say "($guess_no) Please enter a guess:";
  my $guess = <>;
  chomp $guess;

  unless ($guess =~ /^\d+$/) {
    say "Hey, that didn't look like a number!";
    redo GUESS;
  }

  if ($guess == $number) {
    say "Congrats, you were on target!";
    last GUESS;
  } elsif ($guess < $number) {
    say "Nay, your guess was TOO SMALL.";
  } elsif ($guess > $number) {
    say "Nay, your guess was TOO BIG.";
  } else {
    die "Illegal state";
  }

  if ($guess_no == $max_guesses) {
    say "However, you have wasted all your guesses. YOU LOOSE.";
    last GUESS;
  }
}

Example usage:

$ perl guess-the-number.pl
(1) Please enter a guess:
15
Nay, your guess was TOO SMALL.
(2) Please enter a guess:
60
Nay, your guess was TOO BIG.
(3) Please enter a guess:
45
Nay, your guess was TOO BIG.
(4) Please enter a guess:
30
Nay, your guess was TOO SMALL.
(5) Please enter a guess:
38
Congrats, you were on target!

(all other corner cases (too many guesses, non-numbers as input) work as expected)

What did I do differently?

• I didn’t loop while the guess was too small (← bug!). Instead, I did a loop iteration for each guess. However, a while (1) loop would have worked as well.
• I did a sanity check on the input, using a simple regular expression. It asserts that the input will be considered numeric by Perl. Else, you get to redo the guess.
• I initialize all variables as soon as I declare them. This removes any possibilities of uninitialized values popping up in error messages.

• I use proper comparision operators. Perl scalars come in two flavours: stringy and numeric:

  Stringy  Numeric
  lt       <
  le       <=
  eq       ==
  ne       !=
  ge       >=
  gt       >
  cmp      <=>
  

• The say function prints the string like print, but appends a newline. This removes akward \ns at the beginning or the end of the string. It makes reading code easier.