此程序是在linux下的对运算符进行重载，了解运算符重载.-This program is in the linux on the operator for overloading, operator overloading to understand.

C++的运算符重载功能，+ = []可是实现将两个字符串拼接，或者选取字符串中的某个字母-C++ operator overloading function,+ = [], but to achieve the two string concatenation, or choose a letter in a string