编写一个函数，要求读入一个非负整数，然后计算和输出它的阶乘 编写一个函数，估算数学常量e 编写一个函数，估算出e^x的值-Write a function to read in a non-negative integer, then the factorial calculations and output it to write a function, to estimate the mathematical constant e to write a function to est