# Depth First Search (DFS) Program in C

In this tutorial you will learn about Depth First Search (DFS) program in C with algorithm.

Most of graph problems involve traversal of a graph. Traversal of a graph means visiting each node and visiting exactly once. There are two types of traversal in graphs i.e. Depth First Search (DFS) and Breadth First Search (BFS).

It is like tree. Traversal can start from any vertex, say Vi . Vi is visited and then all vertices adjacent to Vi are traversed recursively using DFS. Since, a graph can have cycles. We must avoid revisiting a node. To do this, when we visit a vertex V, we mark it visited. A node that has already been marked as visited should not be selected for traversal. Marking of visited vertices can be done with the help of a global array visited[ ]. Array visited[ ] is initialized to false (0).

## Depth First Search (DFS) Algorithm

The graph shown above is taken as input in both the programs mentioned below:

## Depth First Search (DFS) Program in C [Adjacency List]

If you found anything incorrect or have doubts regarding above Depth First Search (DFS) program in C tutorial then comment below.

## 22 thoughts on “Depth First Search (DFS) Program in C”

1. Varsha Patil

void DFS(int i)
{
node *p;
printf("n%d",i);
p=G[i];
visited[i]=1;
while(p!=NULL)
{
i=p->vertex;
if(!visited[i])
DFS(i);
p=p->next;
}
}
In this function after while loop is terminated how the backtracking is happen?

2. hira naz

i am trying to work with adjacency matrix method in C# but I am unable to use NOT operator with int data type. Can you please elaborate it in C# especially the if condition used in the adjacency matrix's program dfs function

1. Andres Rodriguez

hira naz instead of using an array of ints you just replace it with an array of boolean types and that is it.

3. Zaid Hameed

I am trying to compile this program but it shows [Error] 'malloc' was not declared in this scope. any solution plz?

4. Ankit

Hello,

Can we find loop in the graph by using above implementation with adj matrix? Please guide about that.

5. shubham sharma

it is for undirected graph but replacing (0,1) with (1,0) gives different answer.how to resolve that.

6. Jerlin Angel S.M

I need greedy depth first search algorithm program using dot net

7. Andrew

In your “Depth First Search (DFS) Program in C [Adjacency List]” code the loop on line 57 looks wrong. You initialize G[0] to NULL and then begin inserting all the edges before you finish initializing the rest of G[]. Since you use the variable ‘i’ for both loops you win not continue where you left off, which doesn’t matter since you already inserted the edges. The problem would be if you have less edges than nodes, you may actually delete some edges in your adjacency-list.

8. abiwo

“q=(node*)malloc(sizeof(node));” this is eror in dev c++ whatshal i
do

1. Admin Post author

Just add stdlib.h header file as we have used malloc() function in the program.

9. mohan

we are not getting the output for this programme

1. Alex

Are you sure you understand what DFS does? We start and vertex 0, and we travel on the edge to vertex 1. From vertex 1 we follow the left most edge to the last vertex of the branch which is vertex N. Once all edges leading from Vertex N that lead to an undiscovered vertex are marked. We travel back to the previous vertex which is vertex N-1 of the branch. And continue this method until we are back at vertex 0 and we are done when all edges from Vertex 0 are marked as being discovered.

2. Alex

I would suggest reviewing what Depth First Search is actually doing. The output is correct for Depth First Search

10. jak

why do I feel like the resulting traversal is wrong?
shouldnt it be 01527634 since after visiting 5,(where 5 is adjacent to 1, 2 and 7), then it will push 2 into stack because its still not visited

11. Varun kamani

What if there is character input data instead of an integer.
here you took an integer so you can do this so by visited[i]=1.
What is there is Character??