C Program to find Connected Components in an Undirected Graph

By | 07.06.2017

Connected Components in an Undirected Graph


Write a C Program to find Connected Components in an Undirected Graph. Here’s simple Program to Cout the Number of Connected Components in an Undirected Graph in C Programming Language.


Undirected graph


An undirected graph is graph, i.e., a set of objects (called vertices or nodes) that are connected together, where all the edges are bidirectional. An undirected graph is sometimes called an undirected network. In contrast, a graph where the edges point in a direction is called a directed graph.


Also Read : : C Program to find whether an Undirected Graph is Connected or not

Below is the source code for C Program to find Connected Components in an Undirected Graph which is successfully compiled and run on Windows System to produce desired output as shown below :


SOURCE CODE : :


/* C Program to find connected components in an Undirected Graph */

#include<stdio.h>
#include<stdlib.h>

#define MAX 100

#define initial 1
#define waiting 2
#define visited 3

int n;    /*Number of vertices in the graph*/
int adj[MAX][MAX]; /*Adjacency Matrix*/
int state[MAX]; /*can be initial, waiting or visited*/
int label[MAX]; /*Denotes the Component Number*/

void create_graph();
void BF_Traversal();
void BFS(int v, int component_Num);

int queue[MAX], front = -1,rear = -1;
void insert_queue(int vertex);
int delete_queue();
int isEmpty_queue();

int main()
{
        create_graph();
        BF_Traversal();
}/*End of main()*/

void BF_Traversal()
{
        int v, components = 0;

        for(v=0;v<n;v++)
                state[v] = initial;

        components++;
    BFS(0, components); /*start BFS from vertex 0*/

        for(v=0; v<n; v++)
        {
                if(state[v] == initial)
                {
                        components++;
                        BFS(v, components);
                }
        }
        printf("\nNumber of connected components = %d\n", components);

        if(components == 1)
                printf("\nConnected Graph\n");
        else
                printf("\nNot a Connected Graph\n");

}/*End of BF_Traversal()*/

void BFS(int v, int component_Num)
{
        int i;

        insert_queue(v);
        state[v] = waiting;

        while(!isEmpty_queue())
        {
                v = delete_queue();
                state[v] = visited;
                label[v] = component_Num;
                printf("\nVertex %d  Component = %d\n",v, label[v]);

                for(i=0; i<n; i++)
                {
                        /* Check for adjacent unvisited vertices */
                        if( adj[v][i] == 1 && state[i] == initial)
                        {
                                insert_queue(i);
                                state[i] = waiting;
                        }
                }
        }
        printf("\n");
}/*End of BFS()*/

void insert_queue(int vertex)
{
        if (rear == MAX-1)
                printf("Queue Overflow\n");
        else
        {
                if(front == -1)  /*If queue is initially empty */
                        front = 0;
                rear = rear+1;
                queue[rear] = vertex ;
        }
}/*End of insert_queue()*/

int isEmpty_queue()
{
        if(front == -1 || front > rear )
                return 1;
        else
                return 0;
}/*End of isEmpty_queue()*/

int delete_queue()
{
        int del_item;
        if (front == -1 || front > rear)
        {
                printf("\nQueue Underflow\n");
                exit(1);
        }

        del_item = queue[front];
        front = front+1;
        return del_item;

}/*End of delete_queue() */

void create_graph()
{
        int i,max_edges,origin,destin;

        printf("\nEnter number of vertices : ");
        scanf("%d",&n);
        max_edges = n*(n-1)/2; /*Undirected graph*/

        for(i=1;i<=max_edges;i++)
        {
                printf("\nEnter edge %d( -1 -1 to quit ) : ",i);
                scanf("%d %d",&origin,&destin);

                if((origin == -1) && (destin == -1))
                        break;

                if( origin >= n || destin >= n || origin<0 || destin<0)
                {
                        printf("\nInvalid edge!\n");
                        i--;
                }
                else
                {
                        adj[origin][destin]=1;
                        adj[destin][origin]=1;
                }
        }/*End of for*/
}/*End of create_graph()*/

OUTPUT : :


/* C Program to find connected components in an Undirected Graph */

Enter number of vertices : 6

Enter edge 1( -1 -1 to quit ) : 0 1

Enter edge 2( -1 -1 to quit ) : 0 2

Enter edge 3( -1 -1 to quit ) : 0 3

Enter edge 4( -1 -1 to quit ) : 1 3

Enter edge 5( -1 -1 to quit ) : 3 2

Enter edge 6( -1 -1 to quit ) : -1 -1

Vertex 0  Component = 1

Vertex 1  Component = 1

Vertex 2  Component = 1

Vertex 3  Component = 1


Vertex 4  Component = 2


Vertex 5  Component = 3


Number of connected components = 3

Not a Connected Graph

Process returned 0

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