# C Program to find whether an Undirected Graph is Connected or not

By | 28.05.2017

## Find Undirected Graph is Connected or not

Write a C Program to find whether an Undirected Graph is Connected or not. Here’s simple C Program to find whether an Undirected Graph is Connected or not.

## 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 implement BFS Algorithm for Disconnected Graph

Below is the source code for C Program to find whether an Undirected Graph is Connected or not which is successfully compiled and run on Windows System to produce desired output as shown below :

### SOURCE CODE : :

```/* C Program to find whether an Undirected Graph is Connected or not */

#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 state[MAX]; /*can be initial, waiting or visited*/

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

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

int main()
{
create_graph();
BF_Traversal();

return 0;

}/*End of main()*/

void BF_Traversal()
{
int v;
int connected = 1;

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

BFS(0); /*start BFS from vertex 0*/

for(v=0; v<n; v++)
{
if(state[v] == initial)
{
connected = 0;
break;
}
}

if(connected)
printf("\nGraph is connected\n");
else
printf("\nGraph is not connected\n");
}/*End of BF_Traversal()*/

void BFS(int v)
{
int i;

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

while( !isEmpty_queue() )
{
v = delete_queue( );
state[v] = visited;
printf("%d ",v);

for(i=0; i<=n-1; 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("\nQueue 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;

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
{
}
}/*End of for*/
}/*End of create_graph()*/```

### OUTPUT : :

```/* C Program to find whether an Undirected Graph is Connected or not */

Enter number of vertices : 5

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 ) : 4 4

Enter edge 7( -1 -1 to quit ) : -1 -1
0 1 2 3

Graph is not connected

Process returned 0```

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