insert an element in binary search tree gives stopped working - c

Question

When I call insert(element) function and add element, it gives an error as programme has stopped working.
It gives an error when i add 3rd element in left of root or add an element in right side of root.
please help to solve it.
void insert(int iElement){
if(sRoot==NULL){ //Initially sRoot is NULL
sRoot=(struct Node*)malloc(sizeof(struct Node));
sRoot->iData=iElement;
sRoot->sLeft=NULL;
sRoot->sRight=NULL;
}
else{
struct Node *current=(struct Node*)malloc(sizeof(struct Node));
current->iData=iElement;
current->sLeft=NULL;
current->sRight=NULL;
struct Node *parent;
struct Node *temp;
parent=sRoot;
while(parent!=NULL){
temp=parent;
if(iElement>parent->iData){
parent=parent->sRight;
}
if(iElement<parent->iData){
parent=parent->sLeft;
}
}
if(iElement<temp->iData)
temp->sLeft=current;
else
temp->sRight=current;
}
}

Answer 1

There are two bugs in the function the first is that in the loop there are used two if statements instead of if-else if statements.
while(parent!=NULL){
temp=parent;
if(iElement>parent->iData){
parent=parent->sRight;
}
if(iElement<parent->iData){
parent=parent->sLeft;
}
}
So if the first if statement was executed then parent can be set to NULL. However in the second statement you are trying to access the data member iData for such a NULL pointer.
So there must be at least
while(parent!=NULL){
temp=parent;
if(iElement>parent->iData){
parent=parent->sRight;
}
else if(iElement<parent->iData){
parent=parent->sLeft;
}
}
The second problem with this loop is if the used will supply a duplicate value then this loop will be infinite because the pointer parent is not changed.
Also there will be a memory leak because the memory was already allocated for the pointer current though neither node shall be appended in case of a duplicate value.
So you need to process the case when the user supplied a duplicate value.
The function can be implemented the following way as it is shown in the demonstrative program.
#include <stdio.h>
#include <stdlib.h>
struct Node
{
int iData;
struct Node *sLeft;
struct Node *sRight;
};
struct Node *sRoot = NULL;
int insert( int iElement )
{
int success = 1;
struct Node **current = &sRoot;
while ( success && *current != NULL )
{
if ( iElement < ( *current )->iData )
{
current = &( *current )->sLeft;
}
else if ( ( *current )->iData < iElement )
{
current = &( *current )->sRight;
}
else
{
success = 0;
}
}
if ( success )
{
*current = malloc( sizeof( struct Node ) );
success = *current != NULL;
if ( success )
{
( *current )->iData = iElement;
( *current )->sLeft = NULL;
( *current )->sRight = NULL;
}
}
return success;
}
int main(void)
{
insert( 10 );
insert( 9 );
insert( 11 );
insert( 12 );
insert( 8 );
insert( 7 );
return 0;
}
Take into account that it is a bad idea when a function depends on global variables.
So it is better to declare it like with one more parameter
int insert( struct Node **sRoot, int iElement );

Answer 2

Here is the modified one, explaination I kept in comments.
void insert(int iElement){
if(sRoot==NULL){ //Initially sRoot is NULL
sRoot=(struct Node*)malloc(sizeof(struct Node));
sRoot->iData=iElement;
sRoot->sLeft=NULL;
sRoot->sRight=NULL;
}
else{
struct Node *current=(struct Node*)malloc(sizeof(struct Node));
current->iData=iElement;
current->sLeft=NULL;
current->sRight=NULL;
struct Node *parent;
struct Node *temp;
parent=sRoot;
while(parent!=NULL){ /* it fails when parent is NULL */
if(iElement > parent->iData){
if(parent->sRight ! = NULL)/* need to check if parent->right is null or not */
parent->sRight = current;/*if not NULL then put i
t here */
else
parent = parent->sRight;/* update the parent */
}
if(iElement < parent->iData){
if(parent->sLeft ! = NULL)
parent->sLeft = current;
else
parent=parent->sLeft;
}
}
}
}