sinc(x)

I wanted to define the sinc(x) function:

(C1) sinc(x) := if (x = 0) then 1 else sin(x)/x;

                                                    SIN(x)
(D1)                sinc(x) := IF x = 0 THEN 1 ELSE ------
                                                      x
(C2) sinc(1);

(D2)                                SIN(1)
(C3) sinc(0);

(D3)                                   1

So far so good.  But

(C4) sinc(x);

                                    SIN(x)
(D4)                                ------
                                      x

Well, that's not right.

I must be missing something stupid, but I don't know what it is.

Ray