一般c++的Int型变量为4个字节，做数字比较大整数的阶乘会溢出，本程序利用数组实现大数字的阶乘且可以更改数组的长度-General c++ of the Int variable is 4 bytes, so the number will be relatively large factorial integer overflow, the process utilizes an array to achieve great numbers factorial and can change