编写一个函数，输入n为偶数时，调用函数求1/2+1/4+...+1/n,当输入n为奇数时，调用函数1/1+1/3+...+1/n(利用指针函数)-The preparation of a function, type n is an even number, the call function for 1/2+1/4+...+ 1/n, when n is odd input, call function 1/1+1/3+...+ 1/n (use pointer function)