说明：  有关于vector的程序，用于检测两个vector量是否相同，但是此程序还可以检测两个vector含有多个重复元素的情况并加入了非法输入检测。属于考虑周全的程序。
(This assignment asks students to write a program to find if two vectors have the same elements with the condition that the order and multiplicities are ignored. For requirements, the numbers should be input the keyboard by the user and the length of the vectors are unknown and user-defined. )