A stream is a sequence of characters that are organized into lines,
where each line consists of 0 or more characters and ends with the
newline character, '\n'.
When execution begins, 3 streams are connected to the program,
automatically.
The standard input stream, stdin, is connected to the keyboard
The standard output stream, stdout, is connected to the screen
The standard error stream,stderr, is connected to the screen
Some operating systems, including both UNIX and DOS allow the
standard input stream and the standard output stream to be redirected
to other devices.
Example: You can use UNIX redirection to let the contents of the file,
datafile.dat, feed into the stdin stream, rather than input from the
keyboard, by using the following command :
a.out < datafile.dat
The standard error stream is typically used to print errors.