What is Linux in C programming language

Linux is a clone of the Unix operating system. Its kernel was written from scratch by Linus Torvalds with assistance from a loosely-knit team of programmers across the world on Internet. It has all the features you would expect in a modern OS. Moreover, unlike Windows or Unix, Linux is available completely free of cost. The kernel of Linux is available in source code form. Anybody is free to change it to suit his requirement, with a precondition that the changed kernel can be distributed only in the source code form. Several programs, 

frameworks, utilities have been built around the Linux kernel. A common user may not want the headaches of downloading the kernel, going through the complicated compilation process, then downloading the frameworks, programs and utilities. Hence many organizations have come forward to make this job easy. They distribute the precompiled kernel, programs, utilities and frameworks on a common media. Moreover, 

they also provide installation scripts for easy installations of the Linux OS and applications. Some of the popular distributions are RedHat, SUSE, Caldera, Debian, Mandrake, Slackware, etc. Each of them contain the same kernel but may contain different application programs, libraries, frameworks, installation scripts, utilities, etc. Which one is better than the other is only a matter of taste.

Linux was first developed for x86-based PCs (386 or higher). These days it also runs on Compaq Alpha AXP, Sun SPARC, Motorola 68000 machines (like Atari ST and Amiga), MIPS, PowerPC, ARM, Intel Itanium, SuperH, etc. Thus Linux works on literally every conceivable microprocessor architecture.
Under Linux one is faced with simply too many choices of Linux distributions, graphical shells and managers, editors, compilers, linkers, debuggers, etc. For simplicity (in my opinion) I have chosen the following combination:

Linux Distribution  - Red Hat Linux 9.0
Console Shell        - BASH
Graphical Shell      - KDE 3.1-10
Editor                   - KWrite
Compiler              - GNU C and C++ compiler (gcc)

We would be using and discussing these in the sections to follow.