意外的树遍历

Question

When I am executing my code, I am getting the wrong result for a pre-order traversal of my binary tree. I am expecting that my program print this pre-order 5 -> 4 -> 3 -> 2-> 6 -> 7 -> 8. I am not able to point out my mistake in code. Please tell me where I have made a mistake.

This is my input and output (a sample run):

ENTER THE NODE DATA
5
ENTER YOUR CHOICE
ENTER THE NODE DATA
4
ENTER YOUR CHOICE
ENTER THE NODE DATA
6
ENTER YOUR CHOICE
ENTER THE NODE DATA
3
ENTER YOUR CHOICE
ENTER THE NODE DATA
7
ENTER YOUR CHOICE
ENTER THE NODE DATA
2
ENTER YOUR CHOICE
ENTER THE NODE DATA
8
ENTER YOUR CHOICE
5 -> 4 -> 3 -> 2 -> 8 -> 7 -> 6 ->

This is the code for creating the binary tree and printing a pre-order traversal of the tree.

#include<conio.h>
#include<stdio.h>
#include<stdlib.h>

struct node {
               int data;
               struct node *right;
               struct node *left;
            }  *tmp  = NULL;

typedef struct node NODE;

  NODE *root = NULL;
  NODE *child, *new_node;

 void preorder(NODE *t)
{
     if(t != NULL)
     {
            printf("%d -> ",t->data);
            preorder(t->left);
            preorder(t->right);
     }//IF
 } 
  int main ()
  {
      char choice;
      do{
           new_node = (NODE *)malloc(sizeof(NODE));
           printf("ENTER THE NODE DATA \n");
           scanf("%d",&new_node -> data);

           new_node -> right = NULL;
           new_node -> left  = NULL;

           if(root == NULL)
           {
                   root = new_node;
                   tmp  = new_node;
           }//IF

           else
           {
               child = new_node;

               while(1)
               {
                       if(child -> data < tmp -> data)
                       {
                             if(tmp -> left == NULL)
                              {
                                  tmp -> left = new_node;
                                  break;  
                              }//if2  
                              tmp  = tmp -> left;
                       }//if1

                       if(child -> data > tmp -> data)
                       {
                           if(tmp -> right == NULL)
                           {
                               tmp -> right = new_node;
                               break;
                           }//if4
                           tmp = tmp -> right;
                       }//if3
               }//while
           }//else
           printf("\n ENTER YOUR CHOICE \n");
           choice = getch();
        }//do
         while(choice != 'n');
         preorder(root);
         getch();
         return 0;
  }//main

Answer 1

You didn't reset tmp to be the root in every iteration.

Note that there is no need for variable child at all, as its value is completely identical to that of new_node .

Answer 2

In do while add the following statement.

else {
child=new_node;
tmp=root;
...
...
}

After every loop, tmp value will be changed. We have to check the new value with the root itself.