Question

This is my code:

print('What amount would you like to calculate tax for?  ')
subtotal = gets.chomp
taxrate = 0.078
tax = subtotal * taxrate
puts "Tax on $#{subtotal} is $#{tax}, so the grand total is $#{subtotal + tax}."

First output: What amount would you like to calculate tax for?

Input: 100.

Final output: Tax on $100 is $, so the grand total is $100.

I believe I should be getting a tax rate of $7.79999999 and a grand total of 107.7999999. I’d like to make the code a little better by doing things like stripping the $ from the input, should a user mistakenly enter a $, and rounding up to the nearest cent. First, I need to understand why I’m not getting any output or addition, though, right?

Answer 1

Let us go through your code:

subtotal = gets.chomp

gets.chomp gives you a String so this:

tax = subtotal * taxrate

is using String#* rather than multiplying numbers:

str * integer → new_str

Copy—Returns a new String containing integer copies of the receiver.

But taxrate.to_i will give you zero and any_string * 0 gives you an empty String. So you’re getting exactly what you’re asking for, you’re simply asking for the wrong thing.

You need to convert subtotal to a number with to_i or to_f:

subtotal = gets.to_f # Or gets.to_i

You won’t need the chomp if you use to_i or to_f, those methods will ignore the trailing whitespace on their own.

That should give you a sensible value in tax.