1. Text Files
All the programs you've seen so far have one thing in common: Any data the program uses or calculates is lost when the program ends.
In order for the data to persist, it must be stored in a file on some type of device.
Once the data is stored, it can be used in the future by the same program or other programs.

2. In order to use files for input or output in your program:
#include <fstream.h>
For file output:
Declare a variable of data type ofstream and associate the name of the file to be used: ofstream outfile( "output.txt" );
Use the name of the variable like you use cout: outfile << id << " " << total << endl;
For file input:
Declare a variable of type ifstream and associate the name of the file: ifstream infile( "data.txt" );
Use the name of the variable like you use cin: infile >> hours;
If you specify a file for output, and that file already exists, the existing file will be deleted, and a new empty file will be created.