Use of uninitialized value $guess in numeric lt (<) line 25 in Perl - perl

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.

Answer 2

You didn't mention which line was line #25! That could be important.
However, look at your while statement. Notice you're comparing $guess with $target, but you haven't set $guess yet. That's set inside you're while loop. This is why you're getting the undefined variable.
I also don't see where $counter is set. That could also be an issue.
Let's look at your while loop a bit closer:
while ( $guess < $target ) {
blah, blah, blah
}
Assuming that there's a $guess, you're looping until the user guesses a number bigger than the $target. Is that what you want? No, you stated that you wanted to give the user eight turns, and that's it. What you want is something more along the lines of:
my $count = 1;
while ( $count <= 8 ) {
$count++;
blah, blah, blah
}
A slightly nicer way of doing this is with a for loop:
for ( my $count = 1; $count <= 8; $count++ ) {
blah, blah, blah
}
However, these C-style for loops are so passé. Plus, there's a clearer way of doing this using the 1..8 syntax. This is the same as saying (1, 2, 3, 4, 5, 6, 7, 8). It's clean and easy to understand:
for my $counter (1..8) {
blah, blah, blah
}
(NOTE: Some people use a foreach keyword instead of a for keyword when doing this type of loop to distinguish it from the C-Style for loop. However, some people (cough! Damian Conway, cough!) frown upon the use of foreach since it doesn't really add clarity.)
Let's look at another aspect of your logic:
if ($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 { #Do this if the guess isn't equal to, greater than or less than the target
print "You lose. The number was $target.";
}
When will your else clause be executed? Answer is never. After all, you won't exeucte it unless $guess is neither greater than, equal to, or less than $target. Also, even if you did lose, you're still in that loop.
What you probably want to do is to put the You lose line outside the loop. That way, after the eighth guess and your loop ends, you get the You lose spiel.
Also, let's look at this line:
chomp ( $guess = <> );
print "Enter guess $counter: ";
First, the <> is the null filehandle operator which is very, very different from <STDIN>:
The null filehandle <> is special: it can be used to emulate the behavior of sed and awk, and any other Unix filter program that takes a list of filenames, doing the same to each line of input from all of them. Input from <> comes either from standard input, or from each file listed on the command line. Here's how it works: the first time <> is evaluated, the #ARGV array is checked, and if it is empty, $ARGV[0] is set to "-", which when opened gives you standard input. The #ARGV array is then processed as a list of filenames.
What you want is <STDIN>.
Also notice that you are getting the input before you print out your prompt. You really want to do this instead:
print "Enter guess $counter: ";
chomp ($guess = <STDIN>);
Also, you want to set $| to a nonzero value to turn off buffering. Otherwise, you might still have to enter your $guess before you see the prompt.
Here's the revised program Modern::Perl doesn't work on my system, so I use the three separate pragmas to cover it:
#! /usr/bin/env perl
use strict;
use warnings;
use feature qw(say);
use constant {
UPPER_RANGE => 100,
MAX_GUESSES => 8,
};
$| = 1;
my $target = int ( ( rand UPPER_RANGE ) + 1 );
for my $counter (1..MAX_GUESSES) {
print "Enter guess #$counter: ";
chomp ( my $guess = <STDIN> );
if ($guess == $target) {
say "Congratulations! You guessed the secret number $target in $counter turns";
exit;
}
elsif ($guess > $target) {
say "Your guess, $guess, is too high.";
}
else {
say "Your guess, $guess, is too low.";
}
}
say "You lose. The number was $target.";
A few things I didn't cover:
When doing numeric comparisons, use the == operator and not eq which is for strings.
I use say instead of print when I can. The say command is like print except it automatically puts a NL on the end for me.
Notice the exit; after I stated you won. I want to end my program at that point.
Notice I don't declare all of my variables until I need them. In my program, $guess and $counter only exists inside the for loop while $target exists both inside and outside the for loop.
I use constant to help avoid mysterious numbers. For example, 1..MAX_GUESSES helps me understand that the loop is going to my maximum guess while 1..8 doesn't explain why I'm going to 8. Also, I can simply change my constant and suddenly you have 10 changes of guessing a number between 1 and 1000.

Answer 3

The problem here is that you aren't explicitly initializing your variables. By default, Perl initializes the variables you create with my() to the undef value. So take a look at the following line in your script:
my ($guess,$target,$counter);
This line creates three variables, all of which are set to undef. For more details on the ins and outs of the my() operator, check out the perlsub docs. Here's a relevant quote from that doc page:
The parameter list to my() may be assigned to if desired, which allows
you to initialize your variables. (If no initializer is given for a
particular variable, it is created with the undefined value.)