IOStream: Input/Output from file
C++ has two basic classes to handle files, ifstream and
ofstream. To use them, include the header file fstream.h.
ifstream handles file input (reading from files).
ofstream handles file output (writing to files). The way to
declare an instance of the ifstream or ofstream class is:
           ifstream a_file;
           //or
           ifstream a_file("filename");