Use of inintialized value $ in concatenation (.) Perl - perl

Question

use warnings;
$a = 5;
$c = 3;
$i;
$x = time();
$m = 32;
$caracter_aleatorio;
#caracteres = (A..Z);
print "Ingrese la cantidad de letras que desea generar=> ";
$n = <STDIN>;
sub generadorMultiplicativo{
$numAleatorio = ((($a*$x) + $c) % $m);
$x = $numAleatorio;
}
for($i=1;$i<=$n;$i++){
&generadorMultiplicativo();
$caracter_aleatorio = $caracteres[$numAleatorio];
if($numAleatorio == 0){
$numAleatorio++;
}
if($numAleatorio > 26){
$numAleatorio = $numAleatorio - 5;
}
print"Letra #$i = $caracter_aleatorio\n";
}
<>;
I know this warning is when the variable doesn't have a value, but I´ve tried everything but it´s the same, it´s a generator of "random" letters.
Could you help me?

Answer 1

Always use strict when writing new code.
Uninitialized warnings means that your $caracter_aleatorio variable is undefined, so you should set a default. Undefined variables are usually a sign of buggy code.
Declare your variables using my
One-letter variables should be avoided for maintenance / readability reasons.
No-longer need to call functions with &foo() notation, foo() is fine.
Use quotes around A and Z to generate the range.
Here is an updated version of your code:
use strict;
use warnings;
my $a = 5;
my $c = 3;
my $i;
my $x = time();
my $m = 32;
my $caracter_aleatorio;
my $numAleatorio;
my #caracteres = ('A'..'Z');
print "Ingrese la cantidad de letras que desea generar=> ";
my $n = <STDIN>;
sub generadorMultiplicativo{
$numAleatorio = ((($a*$x) + $c) % $m);
$x = $numAleatorio;
}
for( $i=1; $i<=$n; $i++ ) {
generadorMultiplicativo();
$caracter_aleatorio = $caracteres[$numAleatorio] || 'unknown';
if($numAleatorio == 0){
$numAleatorio++;
}
if($numAleatorio > 26){
$numAleatorio = $numAleatorio - 5;
}
print"Letra #$i = $caracter_aleatorio\n";
}
Suggestions to improve further:
Learn how to accept/return parameters from subroutines. perldoc perlsub
Input validation, what if I pass in 'abc' instead of 123, numeric vs string comparison operators ( <= vs lt, == vs eq, >= vs gt, etc. ).
Write comments to show high level intent of your code.
Provide a usage/help message to show a new user how to use your script.
The perl documentation is excellent, have a read through perldoc perlintro

Answer 2

To see the issue, after you call generadorMultiplicativo(); you can do some debug printing of $numAleatorio to see that it sometimes goes higher than you intend. That is, it can be greater than 25.
print "DEBUG: $numAleatorio of $#caracteres\n";
Your method tries to fix these out of bounds values, but you have some issues:
26 as the upper limit instead of 25
You subtract 5 if above upper bound but sometimes you are more than 5 above upper bound.
Your pseudorandom number generator is generating values too high.
Recommended rewrite:
use strict;
use warnings;
my #caracteres = ('A'..'Z');
print "Ingres la cantidad de letras que desea generar=> ";
while(my $n = <STDIN>) {
last unless $n =~ /^[0-9]+$/; # Check upper limit?
for (1.. $n) {
print "Letras #%d = %s\n", $_, $caracteres[int(rand(26))];
}
}
Does almost the same thing except you can keep asking for more random chars. Just enter non-digit to exit.
First post/answer and typed on my phone so please forgive my mistakes!