More programming challenge stuff.
Converts temperatures in 6 different ways.

#!/usr/bin/perl
use warnings; use strict;

print "1 - Fahrenheit to Celcius\n2 - Celcius to Fahrenheit\n" .
      "3 - Celcius to Kelvin\n4 - Kelvin to Celcius\n" .
      "5 - Fahrenheit to Kelvin\n6 - Kelvin to Fahrenheit\nChoice: ";

chomp(my $choice = <STDIN>);
print "Temperature: ";
chomp(my $temp = <STDIN>);
$temp =~ s/[^0-9]+//g;

if ($choice eq 1) { $temp = ftc($temp); } elsif
   ($choice eq 2) { $temp = ctf($temp); } elsif
   ($choice eq 3) { $temp = ctk($temp); } elsif
   ($choice eq 4) { $temp = ktc($temp); } elsif
   ($choice eq 5) { $temp = ftk($temp); } elsif
   ($choice eq 6) { $temp = ktf($temp); } else {
   print "Invalid choice\n";
}

print "Result: $temp\n";

sub ftc {
    my $temp = $_[0];
    my $rvalue = (($temp - 32) * 5) / 9;
    return $rvalue;
}

sub ctf {
    my $temp = $_[0];
    my $rvalue = (($temp * 9) / 5) + 32;
    return $rvalue;
}

sub ctk {
    my $temp = $_[0];
    my $rvalue = ($temp + 273.15);
    return $rvalue;
}

sub ktc {
    my $temp = $_[0];
    my $rvalue = ($temp - 273.15);
    return $rvalue;
}

sub ftk {
    my $temp = $_[0];
    $temp = ftc($temp);
    $temp = ctk($temp);
    return $temp;
}

sub ktf {
    my $temp = $_[0];
    $temp = ktc($temp);
    $temp = ctf($temp);
    return $temp;
}