temp.rb

class Convert
    @@temp,@@unit = gets.strip.split
    def units
        @@unit
    end
    def temps
        self.is_i?(@@temp)
        @@temp
    end
    def is_i?(s)
        begin
            Integer(s)
        rescue ArgumentError
            puts 'NaN'
        end
    end
    def is_s?(s)
        s.to_s.to_i == s
    end
    def convert(temp, f)
        if f == "C" || f == "c"
            return ((temp.to_i * 9/5) +32).to_s + " " + unit_n(units)
        elsif f == "F" || f == "f"
            return (((temp.to_i - 32) * 5/9).round(2)).to_s + " " + unit_n(units)
        else
            return 0 #raise 'An error has occured'
        end
    end
    def unit_n(unit)
        if @@unit == "F" || @@unit == "f"
            return unit2 = "°C"
        else
            return unit2 =  "°F"
        end
    end

end

x = Convert.new
puts "#{x.temps} °#{x.units} sind #{x.convert(x.temps ,x.units)}"