#!/usr/bin/perl -w
print "Enter the number of teeth on the chainring: ";
chomp ($chainring = <STDIN>);
print "Enter the number of teeth on the cog: ";
chomp ($cog = <STDIN>);
if ($cog <= 0) {
  print "Error: The gear inches cannot be calculated using $cog as a cog value.  Please enter another value.";
} else {
  print "Is your rear wheel metric? (y/n): ";
  chomp ($_ = <STDIN>);
  if ($_ eq "y") {
    print "Enter your metric wheel size in millimeters: ";
    chomp ($metric = <STDIN>);
    $wheel = $metric * .039;
    $gear_inches = ($chainring / $cog) * $wheel;
    print "The gear inches for a chainring of $chainring teeth and a cog of $cog teeth and a wheel of $metric millimeters is $gear_inches gear inches.\n";
  } else {
    print "Enter your wheel size in inches: ";
    chomp ($wheel = <STDIN>);
    $gear_inches = ($chainring / $cog) * $wheel;
    print "The gear inches for a chainring of $chainring teeth and a cog of $cog teeth for a wheel $wheel inches in diameter is $gear_inches gear inches.\n";
  }
}