"wrong number of arguments" ArgumentError when using round

Question

I am trying to convert a temperature from Fahrenheit to Celsius:

puts 'Convertir grados Fahrenheit a Celcius'
STDOUT.flush
x = gets.chomp

aprox = (x * 100.0).round(2) / 100.0

resultado = (aprox-32)/1.8

puts resultado

I use the correct formula for converting Fahrenheit to Celcius:

Celsius = Fahrenheit - 32 / 1.8

However, when I run this in the console, it gives me the following error:

`round': wrong number of arguments (1 for 0) (ArgumentError)

I've tried different things but I don't understand why this doesn't work.

Answer 1

In ruby version prior to 1.9.0 round does not take arguments. It rounds to the nearest integer (see the documentation about floats and the use of round)

Use this instead:

aprox = (x * 100).round() / 100.0

The whole point of multiplying and dividing by 100 is to round the last two digit of x.

Answer 2

You don't specify what version of Ruby you are using. That makes a difference, because in Rubies prior to 1.9 Float#round did not take a parameter. In 1.9+ it does.

>> RUBY_VERSION #=> "1.9.2"
>> pi = 3.141 #=> 3.141
>> pi.round #=> 3
>> pi.round(1) #=> 3.1
>> 3.141.round(1) #=> 3.1

Answer 3

activesupport (part of rails) also gives you Float#round(precision)