Assisstance with comparisons in primitive recursion

Question

I have been given the following question on a tutorial about recursive functions and am not sure how to compare two arguments

  Show that the sign function, sign: N  -> N, is primitive recursive where
            sign(x)=  x>0 : x=1
                      x=0 : x=0
    Note the number of arguments of sign.

I already know that I will use

succ(zero(x)

to assign 1 and

zero(x)

to assign 0 but I do not know compare the x to zero.