# Binary Tree in C Using Recursion

Here you will get program to create binary tree in C using recursion.

What is Binary Tree?

A tree is said to be a binary tree if each node of the tree can have maximum of two children. Children of a node of binary tree are ordered. One child is called left child and the other is called right child. An example of binary tree is shown in below diagram.

Also Read: Binary Search Tree in C

### Creation of Binary Tree Using Recursion

A binary tree can be created recursively. The program will work as follow:

1. Read a data in x.
2. Allocate memory for a new node and store the address in pointer p.
3. Store the data x in the node p.
4. Recursively create the left subtree of p and make it the left child of p.
5. Recursively create the right subtree of p and make it the right child of p.
The program is written in C language which allows linked representation of binary tree. Code will be as follow:

## Program to Create Binary Tree in C Using Recursion

```#include<stdio.h>

typedef struct node
{
int data;
struct node *left;
struct node *right;
} node;

node *create()
{
node *p;
int x;
printf("Enter data(-1 for no data):");
scanf("%d",&x);

if(x==-1)
return NULL;

p=(node*)malloc(sizeof(node));
p->data=x;

printf("Enter left child of %d:\n",x);
p->left=create();

printf("Enter right child of %d:\n",x);
p->right=create();

return p;
}

void preorder(node *t)		//address of root node is passed in t
{
if(t!=NULL)
{
printf("\n%d",t->data);		//visit the root
preorder(t->left);		//preorder traversal on left subtree
preorder(t->right);		//preorder traversal om right subtree
}
}

int main()
{
node *root;
root=create();
printf("\nThe preorder traversal of tree is:\n");
preorder(root);

return 0;
}```

Output

Enter data(-1 for no data):5
Enter left child of 5:
Enter data(-1 for no data):7
Enter left child of 7:
Enter data(-1 for no data):8
Enter left child of 8:
Enter data(-1 for no data):3
Enter left child of 3:
Enter data(-1 for no data):-1
Enter right child of 3:
Enter data(-1 for no data):-1
Enter right child of 8:
Enter data(-1 for no data):-1
Enter right child of 7:
Enter data(-1 for no data):-1
Enter right child of 5:
Enter data(-1 for no data):-1

The preorder traversal of tree is:

5
7
8
3

### Video Tutorial

In the above program I have used preorder traversal to just show that the tree is created properly or not. You can use any other traversal method here. Comment below if you found anything incorrect or missing in above program for binary tree in C.

### 35 thoughts on “Binary Tree in C Using Recursion”

I just modified the program.
Used cout & cin instead of printf & scanf.

I got "malloc undeclared error".
#include

Thank Youu

2. As far as I understand to create above binary tree ABCDEFG. your program needs input in the form
A B D -1 -1 E -1 -1 C F -1 -1 G – 1-1
Can you please provide a program to create ABCDEFG binary tree which take input in this order : A B C D E F G

1. void inorder(node *t)
{
if(t!=NULL)
{
inorder(t->left); //inorder traversal on left subtree
printf(“\n%d”,t->data); // visit the root
inorder(t->right); //inorder traversal om right subtree
}

}

write this code and delete function preorder

1. Can u plz..explain this code
See..here I am confused.
When the recursive function call of inorder(t->left) is done
i.e when t->left=null(at the leftmost node)
then if condition should no longer execute as t=null despite it is, why?

3. To be honest, I found this code a bit complicated and not properly arranged…what,s about the case if you want to insert a new node to the tree???..

1. well traversal function is a kind of function for displaying the tree elements.

4. I was searching for tree creation program for a long time, this one is so neat and nice. Thanks for helping.

1. as we using recursion the time complexity of both create and post order program is n order so n+n is 2n thats O(n)……………….

5. Can anyone explain me this line:
p=(node*)malloc(sizeof(node));
p->data=x; //mainly this line im unalbe to understand this.

6. for dynamic memory allocation stdlib.h header file must be included.
use #include just after #include