Insertion in Binary Search Tree not working

The Insert function works with a copy of the node pointer. So, whatever change you do to that pointer will be on the copy - ie. the change will not be visible in main.

More specifically, this line :

                R=NewNode ;

modifies the local function copy of the node pointer, not the one in main.


I suggest to design your tree such that an empty tree still has a root struct (not a node with a value - simply a struct that contains a pointer to the root). That way, you can pass that root struct (which contains a null pointer) to the Insert function, which can then modify the node pointer inside that struct to point to the newly created root node.

Thanks Infinity08.

>> The Insert function works with a copy of the node pointer
But Why ? i am sending address of pointer in line Insert(&*Root) ;

>> I suggest to design your tree such  . . .
How ?
i tried :
instead of :
struct node
{
      int info;
      struct node *Left, *Right;
} *Root=NULL;

i wrote :
struct node
{
      int info;
      struct node *Left, *Right;
} ;
struct node *Root=NULL;

but it didnt work.


please simplify.

Thanks a lot.

>> But Why ? i am sending address of pointer in line Insert(&*Root) ;

No, you are dereferencing the pointer, and then taking the address. &*Root is the same as just Root.
If you want to pass the address of the pointer, then you need to pass &Root, but then you'd also have to modify the Insert function to accept a struct node** rather than a struct node*.


>> How ?

What I meant is to have another struct called BST (or something similar) :

typedef struct BST {
    struct node *root;
} BST;

This struct represents your BST. When its root member is null, it means the BST is empty. When it's not null, it's pointing to the root node.

ok, i will try it by passing &Root.
Thanks.
and
>>
typedef struct BST {
    struct node *root;
} BST;



Mean while, Please also check my question on VB at :
https://www.experts-exchange.com/questions/23844294/Adding-Picture-Picture-box-to-MDI-Form.html

Thansk a lot.
dont want to do this.

>> ok, i will try it by passing &Root.

It's either one or the other, not both ;) Either the extra struct, or passing &Root. And as I said earlier, I recommend the extra struct.

>> Mean while, Please also check my question on VB . .

Hi Infinity !
as per your suggestion, i have changed my program to following.
BUT, now
     1. It has become very complex.
     2. when i tried to run it, it aborted.
Please check, where i am wrong.
Thanks.

#include<stdio.h>
#include<Conio.h>
 
struct node
{
	int info;
	struct node *Left, *Right;
};
 
typedef struct node BST ;
 
BST *Root=NULL;
 
void Insert(BST**,int);
void Inorder(BST **);
 
void main()
{
	int i, n, item;
	clrscr();
	printf("How many nodes :") ;
	scanf("%d", &n);
	for(i=0;i<n;i++)
	{
		printf("\nEnter Item : ");
		scanf("%d", &item);
		Insert(&Root, item);
		printf("\n %p", &Root);
	}
getch();
}
 
void Insert(struct node **R, int item)
{
	struct node *NewNode ;
	if(R==NULL)
	{
		//Create a new node, add item to it, make its both children NULL.
		NewNode=(struct node*)malloc(sizeof(struct node));
		NewNode->info= item;
		NewNode->Left = NewNode ->Right = NULL ;
		printf("\t%p", NewNode);
		//Make R point to NewNode
		R=&NewNode ;
	}
	else if(item < (*R)->info)
	{
		Insert(&(*R)->Left, item);
	}
	else if(item > (*R)->info)
	{
		Insert(&(*R)->Right, item);
	}
	else
	{
		printf("\nError : Duplicate Item, Cant be inserted ");
	}
}
 
void Inorder(BST **R)
{
	if(R==NULL) return;
	Inorder(&(*R)->Left);
	printf("%d", (*R)->info);
	Inorder(&(*R)->Right);
}

Select allOpen in new window

waiting ...

>>         if(R==NULL)

You need to check whether *R is NULL. *R is the node pointer, not R.


>>                 R=&NewNode ;

No, you have to assign the pointer :

        *R = NewNode;


One more thing : main HAS to return int, not void. You should fix that.

ok, i made these changes.
now, Insert function is running.
BUT still Inorder function is not running.
Also, can this statement
            Insert(&(*R)->Left, item);
in Insert function be simplified ?

>> BUT still Inorder function is not running.

Take a closer look at what it does. And why are you passing a BST** ?

Also : it's your choice not to create a separate BST struct, but it would make things easier.

actually i am not clear about BST *R1and BST **R2.

though i know R1 is pointer to structure of type BST and R2 is Pointer to such pointer.
but why do i need to pass BST ** to Insert and BST *  to Inorder.
why BST * passed to Insert does not act as pointer ?

Please help to understand this, so that i dont trouble again with question as above.


Thanks.

>> why BST * passed to Insert does not act as pointer ?

BST* is a pointer. Inside the function you can modify what that pointer points to.

But the problem is that in the Insert function, you want to modify the pointer itself (not only what it points to). So, you need to pass a pointer to the pointer in order to be able to modify the pointer itself.

You wouldn't need to pass a pointer-to-pointer if you would use a separate BST struct as I suggested a few times already.

hello again.
Please, i have modified code as per my best knowledge and as guided by you.
but still there are some problems,. Inorder() is not working.
program aborts, when i call it from main.
Please Check.

Thanks.

#include<STDIO.h>
#include<iostream.h>
#include<conio.h>
#include<alloc.h>
 
struct node
{
  int info;
  struct node *left,*right;
};
 
struct node *root=NULL;
 
void insert(struct node**, int);
void inorder(struct node*);
void tmp(struct node*) ;
 
 
int main()
{
   clrscr();
   int i, n, item;
   cout<<"\n how many nodes";
   cin>>n;
   for(i=0;i<n;i++)
   {
     cin>>item;
     insert(&root,item);
   }
  // inorder(root);  //Not Working
  tmp(root);   //Giving Wrong OutPut
 
getch();
return 0;
}
 
void tmp(struct node *r)
{
	printf("\n %p  %d  %p", r->left, r->info, r->right);
}
 
void inorder(struct node *r)
{
	if (r==NULL) return;
	inorder(r->left) ;
	printf("%d", r->info);
	inorder(r->right);
}
 
void insert(struct node **r,int val)
{
      struct node *newnode;
      if(*r==NULL)
      {
	       newnode=(struct node*)malloc(sizeof(struct node*));
	       newnode->info=val;
	       newnode->left=NULL ;
	       newnode->right = NULL ;
	       *r = newnode ;
	       printf("\t%p", newnode);
      }
      else if(val < (*r)->info)
	insert(&(*r)->left,val);
      else if(val >  (*r)->info)
	insert(&(*r)->right,val);
      else
	printf("\nDuplicate Error ");
}

Select allOpen in new window

Thanks lot Infinty08 !
oh that was really a stupid misktake.
i will try and revert back.

yes, it worked.
Thanks a lot.