之前在使用# include 定义y1变量时出现下列错误信息

error: previous declaration of ‘double y1(double)’

自动弹出 了 math.h库中的源码解释 CRTIMP double __cdecl j0 (double); _CRTIMP double __cdecl j1 (double); _CRTIMP double __cdecl jn (int, double); _CRTIMP double __cdecl y0 (double); _CRTIMP double __cdecl y1 (double); _CRTIMP double __cdecl yn (int, double);

_CRTIMP double __cdecl chgsign (double);

所以问题出在 math.h 库中

我们能看到 以上变量被征用 ，所以在使用math.h定义时 不能使用上面变量

大佬给出的 解释

Function: double j0 (double x) j0 returns the Bessel function of the first kind of order 0 of x. It may signal underflow if x is too large.

Function: double j1 (double x) j1 returns the Bessel function of the first kind of order 1 of x. It may signal underflow if x is too large.

Function: double jn (int n, double x) jn returns the Bessel function of the first kind of order n of x. It may signal underflow if x is too large.

Function: double y0 (double x) y0 returns the Bessel function of the second kind of order 0 of x. It may signal underflow if x is too large. If x is negative, y0 signals a domain error; if it is zero, y0 signals overflow and returns -∞.

Function: double y1 (double x)y1 returns the Bessel function of the second kind of order 1 of x. It may signal underflow if x is too large. If x is negative, y1 signals a domain error; if it is zero, y1 signals overflow and returns -∞.

Function: double yn (int n, double x)yn returns the Bessel function of the second kind of order n of x. It may signal underflow if x is too large. If x is negative, yn signals a domain error; if it is zero, yn signals overflow and returns -∞.

—— 本文来自火龙信奥（义乌睿码科技）：义乌青少年信息学奥赛与编程教育平台，专注 CSP-J/S、NOIP、GESP 竞赛培训，线上线下融合教学，助力编程升学。网址：hlcoding.com