Variables and Constants:

These are the smallest components of a programming language.  For writing a program, one must know how to use the internal memory of a computer. A Computer memory is divided into several locations where each location has its own address. Memory organization can be represented diagrammatically as below:  

Each location or cell can hold some information. In order to store, retrieve or manipulate data from a specific memory location, we must have some identifier for a particular location. .