C Program: Binary Tree creation with user input

Last update on August 05 2025 12:57:07 (UTC/GMT +8 hours)

1. Binary Tree Construction Variants

Write a C program that creates a binary tree. Allow users to input nodes and build a binary tree structure.

Sample Solution:

C Code:

// Including necessary header files
#include <stdio.h>
#include <stdlib.h>

// Structure for a binary tree node
struct TreeNode {
    int data;
    struct TreeNode* left;
    struct TreeNode* right;
};

// Function to create a new node
struct TreeNode* createNode(int value) {
    // Allocate memory for a new TreeNode
    struct TreeNode* newNode = (struct TreeNode*)malloc(sizeof(struct TreeNode));

    // Check if memory allocation was successful
    if (newNode != NULL) {
        // Initialize node data
        newNode->data = value;
        newNode->left = NULL;
        newNode->right = NULL;
    }

    // Return the created node
    return newNode;
}

// Function to insert a node into the binary tree
struct TreeNode* insertNode(struct TreeNode* root, int value) {
    // If the tree is empty, create a new node
    if (root == NULL) {
        return createNode(value);
    }

    // If the value is less than the root's data, insert into the left subtree
    if (value < root->data) {
        root->left = insertNode(root->left, value);
    }
    // If the value is greater than the root's data, insert into the right subtree
    else if (value > root->data) {
        root->right = insertNode(root->right, value);
    }

    // Return the modified root
    return root;
}

// Function to perform in-order traversal of the binary tree
void inOrderTraversal(struct TreeNode* root) {
    // Traverse the tree in-order: left subtree, root, right subtree
    if (root != NULL) {
        inOrderTraversal(root->left);
        printf("%d ", root->data);
        inOrderTraversal(root->right);
    }
}

// Function to free the memory allocated for the binary tree
void freeTree(struct TreeNode* root) {
    // Recursively free memory for the entire tree
    if (root != NULL) {
        freeTree(root->left);
        freeTree(root->right);
        free(root);
    }
}

int main() {
    // Initialize the root of the binary tree
    struct TreeNode* root = NULL;
    int nodeValue;
    char choice;

    // User input loop to insert nodes into the binary tree
    do {
        // Prompt user for a value to insert into the binary tree
        printf("Input a value to insert into the binary tree: ");
        scanf("%d", &nodeValue);

        // Insert the value into the binary tree
        root = insertNode(root, nodeValue);

        // Ask user if they want to insert another node
        printf("Want to insert another node? (y/n): ");
        scanf(" %c", &choice);

    } while (choice == 'y' || choice == 'Y');

    // Display the in-order traversal of the binary tree
    printf("\nIn-order Traversal of the Binary Tree: ");
    inOrderTraversal(root);
    printf("\n");

    // Free allocated memory for the binary tree
    freeTree(root);

    // Return 0 to indicate successful execution
    return 0;
}

Output:

Input a value to insert into the binary tree: 50
Want to insert another node? (y/n): y
Input a value to insert into the binary tree: 18
Want to insert another node? (y/n): y
Input a value to insert into the binary tree: 73
Want to insert another node? (y/n): y
Input a value to insert into the binary tree: 12
Want to insert another node? (y/n): y
Input a value to insert into the binary tree: 9
Want to insert another node? (y/n): n

In-order Traversal of the Binary Tree: 9 12 18 50 73.

Explanation:

In the exercise above,

Structures:

The program defines a structure "TreeNode" representing a node in the binary tree, containing data, left, and right pointers.

Functions:

createNode(): Allocates memory for a new node and initializes its data.
insertNode(): Inserts a node into the binary tree based on the value, recursively.
inOrderTraversal(): Performs in-order traversal (left subtree, root, right subtree) and prints the data.
freeTree(): Frees the memory allocated for the binary tree.

Main Function:

Initializes the root of the binary tree.
Asks users to input values for nodes in a loop and inserts them into the binary tree.
Displays the in-order traversal of the binary tree.
Frees the allocated memory.

User Interaction:

Users input values to create nodes in the binary tree.
Users decide whether to insert another node (y/n).

Memory Management:

Memory is dynamically allocated for each node and freed at the end to prevent memory leaks.

Execution:

The program performs the specified operations and displays the in-order traversal of the created binary tree.

Flowchart:

Flowchart: C Program: Binary Tree creation with user input.

For more Practice: Solve these Related Problems:

Write a C program to create a binary tree by inserting nodes in level order and display the tree in a structured hierarchy.
Write a C program to construct a binary tree from given pre-order and in-order traversal arrays.
Write a C program to build a binary tree that accepts duplicate values and organizes them by inserting duplicates as right children.
Write a C program to interactively construct a binary tree by letting the user specify parent-child relationships at runtime.

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