*Find Undirected Graph is Connected or not*

*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 : :**

**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 adj[MAX][MAX]; /*Adjacency Matrix*/ 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 { adj[origin][destin] = 1; adj[destin][origin] = 1; } }/*End of for*/ }/*End of create_graph()*/

**OUTPUT : :**

**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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