Bash w/Haskell, 198 <del>275</del>
---

    echo 'u=unwords
    instance Num String where fromInteger=show;a+b=u[a,b,"+"];a-b=u[a,b,"-"];a*b=u[a,b,"*"]
    instance Fractional String where a/b=u[a,b,"/"]
    main=putStr$'$*|runghc -XFlexibleInstances 2>w

Pity, it's longer than the C solution though I was almost as lazy as @Geoff with the bc one...

Takes input as command-line parameters. A file `w` with some ghc warning messages will be created, if you don't like this change to `runghc 2>/dev/null`.