# C Program for Depth First Search or DFS for a Graph

• Last Updated : 20 Dec, 2021

Depth First Traversal (or Search) for a graph is similar to Depth First Traversal of a tree. The only catch here is, unlike trees, graphs may contain cycles, so we may come to the same node again. To avoid processing a node more than once, we use a boolean visited array.

For example, in the following graph, we start traversal from vertex 2. When we come to vertex 0, we look for all adjacent vertices of it. 2 is also an adjacent vertex of 0. If we don\’t mark visited vertices, then 2 will be processed again and it will become a non-terminating process. A Depth First Traversal of the following graph is 2, 0, 1, 3.

See this post for all applications of Depth First Traversal.
Following are implementations of simple Depth First Traversal. The C++ implementation uses adjacency list representation of graphs. STL\’s list container is used to store lists of adjacent nodes.

## C++

 `// C++ program to print DFS traversal for a given given graph``#include``#include         ``using` `namespace` `std;`` ` `class` `Graph``{``    ``int` `V;    ``// No. of vertices``    ``list<``int``> *adj;    ``// Pointer to an array containing adjacency lists``    ``void` `DFSUtil(``int` `v, ``bool` `visited[]);  ``// A function used by DFS``public``:``    ``Graph(``int` `V);   ``// Constructor``    ``void` `addEdge(``int` `v, ``int` `w);   ``// function to add an edge to graph``    ``void` `DFS();    ``// prints DFS traversal of the complete graph``};`` ` `Graph::Graph(``int` `V)``{``    ``this``->V = V;``    ``adj = ``new` `list<``int``>[V];``}`` ` `void` `Graph::addEdge(``int` `v, ``int` `w)``{``    ``adj[v].push_back(w); ``// Add w to vās list.``}`` ` `void` `Graph::DFSUtil(``int` `v, ``bool` `visited[])``{``    ``// Mark the current node as visited and print it``    ``visited[v] = ``true``;``    ``cout << v << ``" "``;`` ` `    ``// Recur for all the vertices adjacent to this vertex``    ``list<``int``>::iterator i;``    ``for``(i = adj[v].begin(); i != adj[v].end(); ++i)``        ``if``(!visited[*i])``            ``DFSUtil(*i, visited);``}`` ` `// The function to do DFS traversal. It uses recursive DFSUtil()``void` `Graph::DFS()``{``    ``// Mark all the vertices as not visited``    ``bool` `*visited = ``new` `bool``[V];``    ``for` `(``int` `i = 0; i < V; i++)``        ``visited[i] = ``false``;`` ` `    ``// Call the recursive helper function to print DFS traversal``    ``// starting from all vertices one by one``    ``for` `(``int` `i = 0; i < V; i++)``        ``if` `(visited[i] == ``false``)``            ``DFSUtil(i, visited);``}`` ` `int` `main()``{``    ``// Create a graph given in the above diagram``    ``Graph g(4);``    ``g.addEdge(0, 1);``    ``g.addEdge(0, 2);``    ``g.addEdge(1, 2);``    ``g.addEdge(2, 0);``    ``g.addEdge(2, 3);``    ``g.addEdge(3, 3);`` ` `    ``cout << ``"Following is Depth First Traversaln"``;``    ``g.DFS();`` ` `    ``return` `0;``}`

Please refer complete article on Depth First Search or DFS for a Graph for more details!

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