补充函数double fun(double x[10])，该函数的功能是求长度为N的一维数组x中元素值的平均值，并对所得结果进行四舍五入（保留两位小数）。-Added function double fun (double x [10]), the demand function is the function of the length of one-dimensional array of N elements in the average value of x, and the resul