C Program to Print All Nodes of a Tree

This is a C Program to print odd levels of the tree. There are basically two functions in this method. One is to print all nodes at a given level (printGivenLevel), and other is to print level order traversal of the tree (printLevelorder). printLevelorder makes use of printGivenLevel to print nodes at all levels one by one starting from root.

Here is source code of the C Program to Print only Odd Numbered Levels of a Tree. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
#include <stdio.h>
```
```
#include <stdlib.h>
```

/* A binary tree node has data, pointer to left child

```
 and a pointer to right child */
```
```
struct node {
```
```
    int data;
```
```
    struct node* left;
```
```
    struct node* right;
```
```
};
```
```
/*Function protoypes*/
```

void printGivenLevel(struct node* root, int level);

```
int height(struct node* node);
```
```
struct node* newNode(int data);
```

/* Function to print level order traversal a tree*/

void printLevelOrder(struct node* root) {

```
    int h = height(root);
```
```
    int i;
```
```
    for (i = 1; i <= h; i += 2)
```
```
        printGivenLevel(root, i);
```
```
}
```
```
/* Print nodes at a given level */
```

void printGivenLevel(struct node* root, int level) {

```
    if (root == NULL)
```
```
        return;
```
```
    if (level == 1)
```
```
        printf("%d ", root->data);
```
```
    else if (level > 1) {
```

        printGivenLevel(root->left, level - 1);

        printGivenLevel(root->right, level - 1);

```
    }
```
```
}
```

/* Compute the "height" of a tree -- the number of

 nodes along the longest path from the root node

```
 down to the farthest leaf node.*/
```
```
int height(struct node* node) {
```
```
    if (node == NULL)
```
```
        return 0;
```
```
    else {
```

        /* compute the height of each subtree */

        int lheight = height(node->left);

        int rheight = height(node->right);

```
        /* use the larger one */
```
```
        if (lheight > rheight)
```
```
            return (lheight + 1);
```
```
        else
```
```
            return (rheight + 1);
```
```
    }
```
```
}
```

/* Helper function that allocates a new node with the

 given data and NULL left and right pointers. */

```
struct node* newNode(int data) {
```

    struct node* node = (struct node*) malloc(sizeof(struct node));

```
    node->data = data;
```
```
    node->left = NULL;
```
```
    node->right = NULL;
```
```
    return (node);
```
```
}
```

/* Driver program to test above functions*/

```
int main() {
```
```
    struct node *root = newNode(1);
```
```
    root->left = newNode(2);
```
```
    root->right = newNode(3);
```
```
    root->left->left = newNode(4);
```
```
    root->left->right = newNode(5);
```

    printf("Level Order traversal of binary tree is(only odd levels) \n");

```
    printLevelOrder(root);
```
```
    return 0;
```
```
}
```

Output:

$ gcc Levelorder.c
$ ./a.out
 
Level Order traversal of binary tree is (only odd levels)
1 4 5

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