C Program to Display Tree Nodes using BFS Traversal

This C Program Display the Nodes of a Tree using BFS Traversal. Breadth-first search (BFS) is a strategy for searching in a graph when search is limited to essentially two operations: (a) visit and inspect a node of a graph; (b) gain access to visit the nodes that neighbor the currently visited node. The BFS begins at a root node and inspects all the neighboring nodes. Then for each of those neighbor nodes in turn, it inspects their neighbor nodes which were unvisited, and so on.

Here is source code of the C Program to Display the Nodes of a Tree using BFS Traversal. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

 * C Program to Display the Nodes of a Tree using BFS Traversal

```
 *                 40
```
```
 *                 /\
```
```
 *                20 60
```
```
 *                /\  \
```
```
 *              10 30  80
```
```
 *                      \
```
```
 *                       90
```
```
 */
```
```
#include <stdio.h>
```
```
#include <stdlib.h>
```
```
 
```
```
struct btnode
```
```
{ 
```
```
    int value; 
```
```
    struct btnode *left, *right; 
```
```
}; 
```
```
typedef struct btnode node;
```
```
 
```
```
/* function declarations */
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void insert(node *, node *);
```
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void bfs_traverse(node *);
```
```
 
```
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/*global declarations */
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node *root = NULL;
```
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int val, front = 0, rear = -1, i;
```
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int queue[20];
```
```
 
```
```
void main() 
```
```
{ 
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```
    node *new = NULL ; 
```
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    int num = 1; 
```

    printf("Enter the elements of the tree(enter 0 to exit)\n");

```
    while (1) 
```
```
    {     
```
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        scanf("%d",  &num); 
```
```
        if (num  ==  0) 
```
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            break; 
```
```
        new = malloc(sizeof(node)); 
```
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        new->left = new->right = NULL; 
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        new->value = num; 
```
```
        if (root == NULL) 
```
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            root = new; 
```
```
        else 
```
```
        { 
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            insert(new, root); 
```
```
        } 
```
```
    }
```

    printf("elements in a tree in inorder are\n");

```
    queue[++rear] = root->value;
```
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    bfs_traverse(root);
```
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    for (i = 0;i <= rear;i++)
```
```
        printf("%d -> ", queue[i]);
```

    printf("%d\n", root->right->right->right->value);

```
}
```
```
 
```
```
/* inserting nodes of a tree */
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void insert(node * new , node *root) 
```
```
{ 
```
```
    if (new->value>root->value) 
```
```
    {     
```
```
        if (root->right == NULL) 
```
```
            root->right = new; 
```
```
        else 
```
```
            insert (new, root->right); 
```
```
    } 
```
```
    if (new->value < root->value) 
```
```
    {     
```
```
        if (root->left  ==  NULL) 
```
```
            root->left = new; 
```
```
        else 
```
```
            insert (new, root->left); 
```
```
    }     
```
```
}
```
```
 
```

/* displaying elements using BFS traversal */

```
void bfs_traverse(node *root)
```
```
{
```
```
    val = root->value;
```

    if ((front <= rear)&&(root->value == queue[front]))

```
    {
```
```
        if (root->left != NULL)
```

            queue[++rear] = root->left->value;

        if (root->right != NULL || root->right  ==  NULL)

            queue[++rear] = root->right->value;

```
        front++;
```
```
    }
```
```
    if (root->left != NULL)
```
```
    {
```
```
        bfs_traverse(root->left);
```
```
    }
```
```
    if (root->right != NULL)
```
```
    {
```
```
        bfs_traverse(root->right);
```
```
    }
```
```
}
```

$ cc tree28.c
$ a.out
Enter the elements of the tree(enter 0 to exit)
40
20
10
30
60
70
80
0
elements in a tree in inorder are
40 -> 20 -> 60 -> 10 -> 30 -> 70 -> 80