Evaluating a string of simple mathematical expressions [closed]

Answer 1

Ruby 1.9

(because of the regex)

Number of characters: 296

def d(s)
  while m = s.match(/((?\((?:\\[()]|[^()]|\g)*\)))/)
    s.sub!(m[:pg], d(m[:pg][1,m[:pg].size-2]))
  end
  while m = s.match(/(-?\d+(\.\d+)?)\s*([*+\-\/])\s*(-?\d+(\.\d+)?)/)
    r=m[1].to_f.send(m[3],m[4].to_f) if %w{+ - * /}.include?m[3]
    s.sub!(m[0], r.to_s)
  end
  s
end

EDIT: Includes Martin's optimization.