In zsh you could use noglob to make this nicer:

  zmodload zsh/mathfunc
  _calc() { echo $[$*] }
  alias c='noglob _calc'

Then:

  % c 2 * atan(1, 0) 
  3.1415926535897931

(Although this works with any command, using an alias with qalc as pointed out above might be more useful.)