auto s = "abcd" creats const char * not string, so use auto with caution.

Since a string in C++ is an array of chars, you can operate it like an array. For example, you can use range-based for loop and so on.

It is recommended that you use std::string in function which are not intended to be interfaces, and you use const char * as parameters of function that are intended to be interfaces (e.g., compiled as shared library and so on).

You can use == to compare whether the content of two std::string are the same, but you cannot use == to compare the content of const char *.