input a number and output the Fibonacci number recursively Perl - perl

Question

For a given value N I am trying to output the corresponding Fibonacci number F(N). My script doesn't seem to enter the recursive stage. fibonnaci($number) is not calling the subroutine. It is simply outputing "fibonacci(whatever number is inputted)".
Here is my code:
#!/usr/bin/perl -w
use warnings;
use strict;
print "Please enter value of N: ";
my $number = <STDIN>;
chomp($number);
sub fibonacci
{
my $f;
if ( $number == 0 ) { # base case
$f = 0;
} elsif ( $number == 1 ) {
$f = 1;
} else { # recursive step
$f = fibonacci( $number - 1 ) + fibonacci( $number - 2 );
}
return $f;
}
print "\nf($number) = fibonacci($number)\n";
Sample Output:
Please enter value of N: 4
f(4) = fibonacci(4)
user1:~>recursiveFib.pl
Please enter value of N: 5
f(5) = fibonacci(5)
user1:~>recursiveFib.pl
Please enter value of N: 10
f(10) = fibonacci(10)
user1:~>
Not sure where I went wrong. Any help would be greatly appreciated.

Answer 1

You need to accept the function arguments properly and take the function call out of the quotes.
use warnings;
use strict;
sub fibonacci {
my ($number) = #_;
if ($number < 2) { # base case
return $number;
}
return fibonacci($number-1) + fibonacci($number-2);
}
print "Please enter value of N: ";
my $number = <STDIN>;
chomp($number);
print "\n$number: ", fibonacci($number), "\n";
A more efficient but still recursive version:
sub fib_r {
my ($n,$a,$b) = #_;
if ($n <= 0) { return $a; }
else { return fib_r($n-1, $b, $a+$b); }
}
sub fib { fib_r($_[0], 0, 1); } # pass initial values of a and b
print fib(10), "\n";

Answer 2

Other answers have already mentioned the lack of taking an argument correctly to the fibonacci function, and that you can't interpolate a function call in the print string like that. Lately my favourite way to interpolate function calls into print strings is to use the ${\ ... } notation for embedding arbitrary expressions into strings:
print "f($number) = ${\ fibonacci($number) }\n";
Other techniques include separate arguments:
print "f($number) = ", fibonacci($number), "\n";
or a helper variable:
my $result = fibonacci($number);
print "f($number) = $result\n";
or even printf:
printf "f(%d) = %d\n", $number, fibonacci($number);
Of all these techniques I tend to prefer either of the first two, because they lead to putting the expressions "in-line" with the rest of the text string, whereas in the latter two they sit elsewhere, making it harder to see at a glance what gets printed where. Especially with printf's positional arguments, it can be easy to be "off-by-one" with a large number of arguments, and put everything in the wrong place.

Answer 3

You are printing in wrong way. you just need to handle the return value. Also the way you are using Number in the sub is also not seems relevant. I have updated the and its working fine.
Also the values that you wanted to print is depend on the start up of the series. whether you want to start from 0 or 1.
The series example start with 1 is 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, so if you put 10 you will get 55.
#!/usr/bin/perl -w
use warnings;
use strict;
print "Please enter value of N: ";
my $number = <STDIN>;
chomp($number);
my $result=fibonacci($number);
sub fibonacci
{
my $f =0;
if ($_[0] == 1 ) { # base case
$f = 1;
} elsif ( $_[0] == 2 ) {
$f = 1;
} else { # recursive step
$f= fibonacci( $_[0] - 1 ) + fibonacci( $_[0] - 2 );
}
return $f;
}
print "\nf($number) = $result\n";