Thread: printing binary trees

I am still relatively new to C Programming (In my second semester in school) an d we are starting binary trees. I can add to my tree and delete from my tree, but whenever I try to print it gives me a segmentation fault (core dump). Here is the code for my printing functions (ascending and descending).

Code:

void LNR(binarytree bt){
LNR(bt->left);
printf("%d", bt->data);
LNR(bt->right);
}


void RNL(binarytree bt){
RNL(bt->right);
printf("%d", bt->data);
RNL(bt->left);
}

Thank you in advance for any help.

Originally Posted by Salem

Somewhere, you need
if ( bt == NULL ) return;
before trying to dereference it.

All right, I edited my code as you suggested and I no longer get a segmentation fault, but it says in my warnings that the (is_empty) function will always return true and it does. Every time I try to print is says it is empty. Normally this would lead me to believe that my function that adds numbers to the tree wasn't working properly, but every time I add numbers my delete function is able to delete them and it says "that number is not in the tree" when I try to delete something that isn't there. So now i am doubly confused. I will post all of my code so you can see what I am talking about..

this is my main.c

Code:

#include <stdio.h>
#include <stdlib.h>
#include "bt.h"
#include "boolean.h"


//  Anthony Cloutier
//  MTW 9:00 Computer Programming II


int menu (void);


int
main (void)
{


  boolean quit = FALSE;
  int selection, num;
  binarytree bt;


  init_tree (&bt);
  menu ();


  while (!quit)
    {
      scanf ("%d", &selection);
      switch (selection)
	{
	case 1:
	  if (is_full ())
	    {
	      printf ("Cannot add another value. It is already full\n");
	    }
	  else
	    {
	      printf ("Please enter the number you would like to add ");
	      scanf ("%d", &num);
	      add (&bt, num);
	    }
	  break;
	case 2:
	  if (is_empty (bt))
	    {
	      printf ("Cannot remove a value. There are none to remove.\n");
	    }
	  else
	    {
	      printf ("What number would you like to delete? ");
	      scanf ("%d", &num);
	      delete_node (&bt, num);
	    }
	  break;
	case 3:
	  if (is_empty (bt))
	    {
	      printf ("There is nothing to print\n");
	    }
	  else
	    {
	      LNR (bt);
	    }
	  break;
	case 4:
	  if (is_empty (bt))
	    {
	      printf ("There is nothing to print\n");
	    }
	  else
	    {
	      RNL (bt);
	    }
	  break;
	case 5:
	  quit = TRUE;
	  break;
	default:
	  printf
	    ("Error: that is not a valid selection. Please try again.\n");
	  break;
	}
      if (!quit)
	{
	  menu ();
	}
    }
  printf ("Have a nice day!\n");
}


int
menu ()
{
  printf ("Please select from one of the following options:\n");
  printf ("1. Add\n2. Delete\n3. Print LNR\n4. Print RNL\n5. Quit\n\n");
  printf ("Please enter your selection ");
}

This is my bt.c (with all my subprograms)

Code:

#include <stdio.h>
#include <stdlib.h>
#include "bt.h"
#include "boolean.h"


void init_tree(binarytree *bt) {
	(*bt) = NULL;
}


boolean is_full(void) {
	binarytree temp;
	temp = (binarytree) malloc (sizeof(struct treenode));
	if (temp == NULL)
	  return TRUE;
	else{
	  free (temp);
	  return FALSE;
}
}


boolean is_empty(binarytree bt) {
  if (bt == NULL)
	return TRUE;
  else
	return FALSE;
}


void add(binarytree *bt, int num){
if((*bt)==NULL){
(*bt)=(binarytree)malloc(sizeof(struct treenode));
(*bt)->left=NULL;
(*bt)->right=NULL;
(*bt)->data=num;
}
else if (num<=(*bt)->data){
add(&(*bt)->left, num);
}
else{
add(&(*bt)->right, num);
}
}


void LNR(binarytree bt){
if (is_empty){
  printf("The tree is empty\n");
}
else{
LNR(bt->left);
printf("%d", bt->data);
LNR(bt->right);
}
}


void RNL(binarytree bt){
if (is_empty){
  printf("The tree is empty\n");
}
else{
RNL(bt->right);
printf("%d", bt->data);
RNL(bt->left);
}
}


void delete_node(binarytree *bt, int num){
binarytree temp;
if((*bt)!=NULL){
  if((*bt)->data==num){
    if(((*bt)-> left == NULL)&&((*bt)->right==NULL)){
      temp = (*bt);
      (*bt) = NULL;
      free(temp);
    }
    else if(((*bt)-> left != NULL)&&((*bt)->right==NULL)){
      temp = (*bt);
      (*bt) = (*bt)->left;
      free(temp);
    }
    else if(((*bt)-> left==NULL)&&((*bt)->right!=NULL)){
      temp = (*bt);
      (*bt) = (*bt)->right;
      free(temp);
    }
    else if(((*bt)-> left!=NULL)&&((*bt)->right!=NULL)){
      temp = ((*bt)->right);
      while(temp->left!=NULL){
        temp = (*bt)->left;
      }
      temp->left = (*bt)->left;
      temp = (*bt);
      (*bt) = (*bt)->right;
      free(temp);
    }
  }
  else if(num<=((*bt)->data)){
    delete_node(&(*bt)->left, num);
  }
  else {
    delete_node(&(*bt)->right, num);
  }
}
else{
printf("That number is not in the tree\n");
}
}

and this is my bt.h

Code:

#include "boolean.h"


#ifndef STACK_H
#define STACK_H


typedef struct treenode{
  int data;
  struct treenode *left, *right;
}*binarytree;


#endif


void init_tree(binarytree *);
boolean is_empty(binarytree);
boolean is_full(void);
void add(binarytree *, int);
void delete_node(binarytree *, int);
void LNR(binarytree);
void RNL(binarytree);

Okay, I just realized I have a check for is_empty() in both my main and my subprogram for printing so i removed the one in my subprogram and I get the segmentation fault back? How does this make sense? I have an if else statement saying if it's empty print an error, otherwise run the program. It shoudn't even run the subprogram if it is empty. Can anyone explain this to me?