Convert cents into dollar string in Ruby without use of BigDecimal

As Micheal Kohl already answered: Take a look to the money gem.

Example:

require 'money'Money.use_i18n = false  #https://stackoverflow.com/q/31133229/676874puts Money.new( 99, 'USD')puts Money.new(324, 'USD')

The following seems to work, but is it correct?

(cents.to_i/100.0).to_s

On the first look, it is ok, but:

cents = '10'p (cents.to_i/100.0).to_s # -> '0.1'

You don't have 2 digits.

Alternative:

p '%.2f' % (cents.to_i/100.0) # -> '0.10'

If they're stings already you could use string manipulation and bypass the numeric problems completely:

# There are, of course, all sorts of ways to do this.def add_decimal(s)  pfx = [ '0.00', '0.0', '0.' ]  if(pfx[s.length])    s = pfx[s.length] + s  else    s = s.dup    s[-2, 0] = '.'  end  sendadd_decimal('')      #   "0.00" add_decimal('1')     #   "0.01" add_decimal('12')    #   "0.12" add_decimal('123')   #   "1.23" add_decimal('1234')  #  "12.34" add_decimal('12345') # "123.45"

No precision issues, no floating point, no bignums, no Rational, nothing tricky, nothing clever. Some simple modifications would be needed to deal with negative values but that will be as simple as what's already there.

You can consider using Rationals as well. However, I am not sure do they get converted to floats when sprintf-ed:

"%.2f" % Rational("324".to_i,100)#=> "3.24""%.2f" % Rational("99".to_i,100)#=> "0.99""%.2f" % Rational("80".to_i,100)#=> "0.80""%.2f" % Rational("12380".to_i,100)#=> "123.80"