A program therefore no longer consists of only one single part. The main program coordinates calls to procedures in separate modules and hands over appropriate data as parameters. Each module can have its own data. This allows each module to manage an internal state which is modified by calls to procedures of this module. However, there is only one state per module and each module exists at most once in the whole program.
Programs use data structures to store data.
Several data structures exist, for example lists, trees, arrays, sets, bags or queues to name a few. Each of these data structures can be characterized by their structure and their access methods . You all know singly linked lists which use a very simple structure, consisting of elements which are strung together, as shown in Fig. Structure of a singly linked list. Singly linked lists just provides access methods to append a new element to their end and to delete the element at the front.