#!/usr/bin/perl
use strict;
use warnings;
 
my $voltage;
my $current;
my $resistance;

print "I will calculate whatever
you specify according to Ohm's law. 
What shall I calculate? \n";

menu();

sub menu() {
print "\n";
print <<EOF;
Press 1 for voltage.
Press 2 for current.
Press 3 for resistance.
Press x to Exit.
EOF

my $selection = <STDIN>;
     chomp $selection;

if ($selection == 1) {voltage();}
elsif ($selection == 2) {current();}
elsif ($selection == 3) {resistance();}
elsif ($selection =~ /x,X/ {all_done();}
else {print "\nSorry, that isn't on the menu. Try again!\n";}
menu();
}