[SOLVED] I tried using this code for creating and displaying a binary search tree...

mscoder · 07-18-2011, 11:46 PM

But it always displays the message for an "empty treee" when i call the display()...

Code:

#include<stdio.h>
#include<malloc.h>


struct node
	{ int data;
	  struct node *lchild;
	  struct node *rchild;
	}*root;


struct node * add(int,struct node *);
void display(struct node *,int);


int main()
{
	int i,n;
	root=NULL;
	do
	{
	printf("1)Add 2)Display 3)Quit");
	printf("\nEnter your choice:\n");
	scanf("%d",&i);
	switch(i)
	{
		case1:  printf("\nEnter the elememt to be addeed to the bst");
			scanf("%d",&n);
			root=add(n,root);  break;

		case 2: if(root==NULL)
			printf("\nEmpty tree"); /*This is the message whenever
			else                      display() called*/
			{
				display(root,1);
			}	
			break;


		case 3:  break;


		default: printf("\nInvalid Choice");
	}
	}while(i!=3);
	
	return(0);
}

struct node *add( int n,struct node *t_start)
{
	struct node *t=t_start;
	if(t==NULL)
	{	
		struct node *tmp=malloc(sizeof(struct node));
		tmp->data=n;
		tmp->lchild=tmp->rchild=NULL;
		t=tmp;		
	}
	else
	{
		if(n<(t->data))
		{	
			t->lchild=add(n,t->lchild);
		}
		else if(n>(t->data))
		{
			t->rchild=add(n,t->rchild);
		}
	}

return(t_start);
}
	
void display(struct node *t,int level)
{
	int i;
	if(t);
	{
		display(t->rchild,level+1);
		printf("\n");
		for(i=0;i<level;i++)
		{
		printf(" ");
		printf("%d",t->data);
		display(t->lchild,level+1);
		}
	}
}

Help me finding the error in the code........

paulsm4 · 07-19-2011, 01:32 AM

Hint:
Is "t" in your add() function ever actually NULL?
(trick question: the answer is "no, it isn't").

Suggestion:
Step through the code under the debugger.

If you're using "gcc", then "gdb" is a good choice of debugger:

http://cs.baylor.edu/~donahoo/tools/gdb/tutorial.html
<= One of many short, simple tutorials you can find.

Single step through the code (you won't have to go far).

Print out the values of key variables (like "t", when it's passed into "add()").

You should have your binary tree working in no time

johnsfine · 07-19-2011, 05:11 AM

Quote:

Originally Posted by mscoder

Code:

        if(n<(t->data))
        {    
            t->lchild=insert(n,t->lchild);
        }
        else if(n>(t->data))
        {
            t->rchild=insert(n,t->rchild);
        }

Help me finding the error in the code........

What is the insert function called from add? It looks like you intended to recursively call add.

johnsfine · 07-20-2011, 09:56 AM

Quote:

Originally Posted by mscoder

Code:

struct node *add( int n,struct node *t_start)
{
    struct node *t=t_start;
    if(t==NULL)
    {    
        struct node *tmp=malloc(sizeof(struct node));
        tmp->data=n;
        tmp->lchild=tmp->rchild=NULL;
        t=tmp;        
    }
...
return(t_start);
}

Notice that you create the new node and point to it using the variable t, but you return t_start, which is still NULL.

Quote:

Help me finding the error in the code.

I assume that you were the one who flagged the first two replies as not helpful. Both were constructive replies from which you should have gotten guidance. Flagging them as not helpful does not improve your chances of getting more help (though this time, I chose to overlook that).

Also, you edited only your original post to correct the error I pointed out in my original reply. An edit to just the original post is very easy to miss in this forum. You should have replied to my reply to at least acknowledge that you corrected that error (and to ask for more help, since it wasn't the only error you needed to correct).