Deletion of node in Binary Search Tree is throwing error - c

Question

Experts, this is my code of creation and deletion of nodes in Binary Search Tree. It's working fine for insertion, but throwing segmentation fault (core dumped) when trying to delete a node (on invoking deleteNode( ) function). I don't understand what's actually the problem. Please help! Thank you in advance!
#include <stdio.h>
#include <stdlib.h>
int size = 0;
typedef struct mylist{
int data;
struct mylist *left;
struct mylist *right;
}node;
node *root;
void create_root(node *root){
root = NULL;
}
//Inserting nodes
node* insert(node *root, int val){
node *ptr, *parentptr, *nodeptr;
ptr = (node*)malloc(sizeof(node));
ptr -> data = val;
ptr -> left = NULL;
ptr -> right = NULL;
if(root == NULL)
root = ptr;
else{
parentptr = NULL;
nodeptr = root;
while(nodeptr != NULL){
parentptr=nodeptr;
if(val < nodeptr -> data)
nodeptr = nodeptr -> left;
else
nodeptr = nodeptr -> right;
}
if(val < parentptr -> data)
parentptr -> left = ptr;
else
parentptr -> right = ptr;
}
return root;
}
node* minValueNode(node* root)
{
node* cur = root;
while (cur->left != NULL)
cur = cur->left;
return cur;
}
node* deleteNode(node* root, int key)
{
if (root == NULL){
printf("\nValue not found\n");
}
if (key < root-> data)
root->left = deleteNode(root->left, key);
else if (key > root-> data)
root->right = deleteNode(root->right, key);
else
{
if (root->left == NULL)
{
node *temp = root->right;
free(root);
return temp;
}
else if (root->right == NULL)
{
node *temp = root->left;
free(root);
return temp;
}
node* temp = minValueNode(root->right); //Inorder successor
root->data = temp->data;
root->right = deleteNode(root->right, temp->data);
}
return root;
}
void main(){
int option, val;
node *ptr;
int flag = 1;
create_root(root);
while(flag != 2){
printf("\nChoose-\n1-Insert\n2-Delete\n3-Exit\n");
scanf("%d", &option);
switch(option){
case 1:{
printf("\nEnter the value of new node\n");
size++;
scanf("%d", &val);
root = insert(root, val);
break;
}
case 2:{
int k;
printf("Enter the value to delete");
scanf("%d",&k);
root=deleteNode(root, k);
size--;
break;
}
case 3:
flag=2;
break;
default:
printf("\nWrong entry\n");
}
}
}

Answer 1

You must either return NULL in the first if() in deleteNode(), or you must put an else before the second if()
node* deleteNode(node* root, int key)
{
if (root == NULL){
printf("\nValue not found\n");
return NULL; // <== This was missing.
}
...
}
or alternatively (perhaps intended?):
node* deleteNode(node* root, int key)
{
if (root == NULL){
printf("\nValue not found\n");
}
else if(key < root->data)
...
}
At the moment this falls through to the next if(key < root->data) even when root is null, which causes the segfault.
Also: Use nullptr if you can use C++11.