Graph implementation using C++

graph_101.cpp

/*
    Graph implementation following  tutorial http://www.geeksforgeeks.org/graph-and-its-representations/
*/
#include<iostream>
#include<cstdlib>
using namespace std;

//struct for an adjacency list node
struct AdjListNode{
    int data;
    AdjListNode *next;
};

//struct for an adjacency list
struct AdjList{
    AdjListNode *head;  //pointer to head node of list
};

//struct for a graph. A graph as an array of adjacency lists
//Size of array will be V (total vertices)
struct Graph{
    int V;
    AdjList *arr;
};

AdjListNode *newAdjListNode(int);
Graph *createGraph(int);
void addEdge(Graph*,int,int);
void printGraph(Graph*);

int main(){
//create a new graph
    int totalVertices=4;
    Graph *graph;
    graph=createGraph(totalVertices);
    //connect edges
    addEdge(graph,0,1);
    addEdge(graph,0,2);
    addEdge(graph,0,3);
    addEdge(graph,1,3);
    addEdge(graph,2,3);
    /*
    addEdge(graph,0,1);
    addEdge(graph,0,4);
    addEdge(graph,1,2);
    addEdge(graph,1,3);
    addEdge(graph,1,4);
    addEdge(graph,2,3);
    addEdge(graph,3,4);
    */
    //print the adjacency list representation of graph
    printGraph(graph);
}

//create a new node
AdjListNode* newAdjListNode(int data){
    AdjListNode *nptr=new AdjListNode;
    nptr->data=data;
    nptr->next=NULL;
    return nptr;
}

//function to create a graph of V - vertices
Graph* createGraph(int V){
    Graph *graph=new Graph;
    graph->V=V;
    //create an array of adjacency list. size of array - V
    graph->arr=new AdjList[V];
    //initialize with NULL (e.g root=NULL)
    for(int i=0;i<V;i++){
        graph->arr[i].head=NULL;
    }
    return graph;
}

//add an edge to an undirected Graph
void addEdge(Graph *graph,int src,int dest){
    //Add an edge from src to dest. A new node added to the adjacency list of src
    //node added at beginning
    AdjListNode *nptr=newAdjListNode(dest);
    nptr->next=graph->arr[src].head;
    graph->arr[src].head=nptr;
    //connect from dest to src (since undirected)
    nptr=newAdjListNode(src);
    nptr->next=graph->arr[dest].head;
    graph->arr[dest].head=nptr;
}

//function to print the graph
void printGraph(Graph* graph){
//loop over each adjacent list
    for(int i=0;i<graph->V;i++){
        AdjListNode *root=graph->arr[i].head;
        cout<<"Adjacency list of vertex "<<i<<endl;
        //loop over each node in list
        while(root!=NULL){
            cout<<root->data<<" -> ";
            root=root->next;
        }
        cout<<endl;
    }
}