Why does this crash??

code:

#include <iostream.h>
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <ctype.h>
#include <string.h>
#include <dos.h>


class tnode
{
public:
int nodevalue;
tnode *left, *right;

//Constructor
tnode (int item, tnode *lptr = NULL,tnode *rptr = NULL)
{
nodevalue=item;
left=lptr;
right=rptr;
}

};

tnode *maxnode=NULL;

void findmaxvalue(tnode* tempnode)
{
if (tempnode!=NULL)
{
if (tempnode->nodevalue > maxnode->nodevalue)
{
maxnode=tempnode;
}
findmaxvalue(tempnode->left);
findmaxvalue(tempnode->right);
}
}

int main()

{

system("CLS");
//Building the tree
tnode *b,*c,*d,*e,*f,*root;
d= new tnode(5);
e= new tnode(38);
f= new tnode(42);
b= new tnode(15, d);
c= new tnode(40,e,f);
root=new tnode(35,b,c);

findmaxvalue(root);
cout<<"\n The maximum value in the tree is :: "<< maxnode->nodevalue;
getch();
return 0;
}

/code

You have to initialize maxvalue before you access it. It's still NULL when you first access it in findmaxvalue.

You lost me......

Code:

---

void findmaxvalue(tnode* tempnode)
{
if (tempnode!=NULL)
{
if (tempnode->nodevalue > maxnode->nodevalue)

---

The first time you call findmaxvalue, maxnode is NULL. So when it attemts to find maxnode->nodevalue, it will throw an error. Try having 'tnode maxnode = root;' instead of =NULL.

Changing
tnode *maxnode=NULL;
to
tnode *maxnode=root;

errors: root' : undeclared identifier
and

'initializing' : cannot convert from 'int' to 'class tnode *'

what did I miss ??

I got it now! Thanks a ton!!

Actually there is quite many errors in your code but dont worry, we will help you :D.

The problem lies in your finmaxvalue

Code:

---

void findmaxvalue(tnode* tempnode)
{
if (tempnode!=NULL)
{
if (tempnode->nodevalue > maxnode->nodevalue)
{
maxnode=tempnode;
}
findmaxvalue(tempnode->left);
findmaxvalue(tempnode->right);
}
}

---

To find the maximum value in a B-Tree is easy (both with recursion or iteration, I´ll use recusrion here). What you really want to find is the element which is the most rightfar in the tree.
In other words

Code:

---

void findmaxvalue(tnode* tempnode)
{

        /* You have a root node which is NULL */
        if (tempnode == NULL)
                return ;

        /* Reached 'last rightmost' (your case 42) element */
        if (tempnode->right == NULL)
        {
                maxnode = tempnode;
                return ;
        }
/* Pass next right childen to findmaxvalue recursivly */
findmaxvalue(tempnode->right);
}

---

I´ll leave findminvalue as an exercise for you to figure out (almost identical with findmaxvalue).

Why not implement a B-Tree with class and high-level functions for it???

Also read this and this before posting next time.