Binary Search Tree in C Data Structure

In computer science, a binary search tree (BST) is a node based binary tree data structure which has the following properties:

• The left subtree of a node contains only nodes with keys less than the node's key.
• The right subtree of a node contains only nodes with keys greater than the node's key.
• Both the left and right subtrees must also be binary search trees.

From the above properties it naturally follows that: Each node (item in the tree) has a distinct key.

Generally, the information represented by each node is a record rather than a single data element. However, for sequencing purposes, nodes are compared according to their keys rather than any part of their their associated records.

The major advantage of binary search trees over other data structures is that the related sorting algorithms and search algorithms such as in-order traversal can be very efficient.

Binary search trees are a fundamental data structure used to construct more abstract data structures such as sets, multisets, and associative arrays.

A binary search tree of size 9 and depth 3, with root 8 and leaves 1, 4, 7 and 13 

#include<stdio.h>
#include<conio.h>
#define null 0

struct t
{
 int data;
 struct t *left;
 struct t *right;
};

typedef struct t tree;
tree *ptr, *root, *q;

void inorder(tree *ptr); //left - root - right
void preorder(tree *ptr); //root - left - right
void postorder(tree *ptr); //left - right - root

void main()
{
 int val;
 char c='n';
 root = (tree *)malloc(sizeof(tree));

 clrscr();

 printf("Enter data: ");
 scanf("%d",&root->data);
 root->left=null;
 root->right=null;
 ptr=root; //set the current pointer to root

 fflush(stdin);
 printf("\nDo you want to add more nodes? (y/n)");
 c=getche();

 while(c!='n')
 {
  printf("\nEnter data: ");
  scanf("%d",&val);
  ptr=root;   //Every time start from root and traverse
  while(1)
  {
   if(val<ptr->data)
   {
    if(ptr->left==null)
    {
     q=(tree *) malloc(sizeof(tree));
     ptr->left=q;
     ptr=ptr->left;
     ptr->data=val;
     ptr->left=null;
     ptr->right=null;
     break;
    }
    else
     ptr=ptr->left;
   }
   else
   {
    if(ptr->right==null)
    {
     q=(tree *) malloc(sizeof(tree));
     ptr->right=q;
     ptr=ptr->right;
     ptr->data=val;
     ptr->left=null;
     ptr->right=null;
     break;
    }
    else
     ptr=ptr->right;
   }
  }

  printf("\nDo you want to add more nodes? (y/n)");
  c=getche();
 }

 printf("\n\n\n\n\nInorder:\n");
 inorder(root);

 printf("\n\nPreorder:\n");
 preorder(root);

 printf("\n\nPostorder:\n");
 postorder(root);

 getch();
}

void inorder(tree *ptr)
{
 //left - root - right
 if(ptr!=null)
 {
  inorder(ptr->left);
  printf("%d\t",ptr->data);
  inorder(ptr->right);
 }
}

void preorder(tree *ptr)
{
 //root - left - right
 if(ptr!=null)
 {
  printf("%d\t",ptr->data);
  inorder(ptr->left);
  inorder(ptr->right);
 }
}

void postorder(tree *ptr)
{
 //left - right - root
 if(ptr!=null)
 {
  inorder(ptr->left);
  inorder(ptr->right);
  printf("%d\t",ptr->data);
 }
}