"graph.h" represents the ADT(Abstract Data Type) of graph data structure.
graph.h consists of a class "graph" which contains the basic functions that a graph needs.
  Basic functions :
    buildgraph -> to build a graph from given input
    display -> displays the data present in the node
    initial -> to initialise the graph
    etc.,

graph.cpp consists of the definitions of the functions that are declared in graph.h (user defined) library.
