C Input and Output

1. Data can come from some location external to the program. Data moved from an external location into RAM, where the program can access it, is called input. The keyboard and disk files are the most common sources of program input.
2. Data can also be sent to a location external to the program; this is called output. The most common destinations for output are the screen, a printer, and disk files.

Input sources and output destinations are collectively referred to as devices. The keyboard is a device; the screen is a device, and so on. Some devices (the keyboard) are for input only, others (the screen) are for output only, and still others (disk files) are for both input and output. Whatever the device, and whether it’s performing input or output, C carries out all input and output operations by means of streams.

What is a Stream?

A stream is a sequence of characters. More exactly, it is a sequence of bytes of data. A sequence of bytes flowing into a program is an input stream; a sequence of bytes flowing out of a program is an output stream. By focusing on streams, we don’t have to worry as much about where they’re going or where they originated.

The major advantage of streams, therefore, is that input/output programming is device independent. Programmers don’t need to write special input/output functions for each device (keyboard, disk, and so on). The program sees input/output as a continuous stream of bytes no matter where the input is coming from or going to.