Linked List from Linked List - c

Question

I am trying to create an (ordered) linked list of (ordered) linked lists. The list-of-list links are carried by the first nodes of its member lists. I am trying to achieve this via the following code, but my program crashes when I try displaying the second list. First list displays perfectly.
Here's a schematic of the data structure I am trying to construct:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
struct node{
int number;
struct node*next;
struct node*lsnext;
};
typedef struct node Node;
Node* insertValue(Node * list, int value);
void display(Node*);
Node* insertArr(Node * list, int value);
Node* addNodeBottom(int val, Node *start);
int main()
{
Node *globalList = NULL, *lists,*start,*save;
int nbrOfLists, listNo, nbrOfVal, valNo, val;
start=NULL;
printf("\n Enter the number of lists:");
scanf("%d", &nbrOfLists);
if(nbrOfLists < 0)
return -1;
for(listNo = 0; listNo < nbrOfLists; listNo++)
{
printf("\n\n Enter the number of inputs to the list %d: \n ",listNo+1);
scanf("%d", &nbrOfVal);
lists = NULL;
for(valNo = 0; valNo < nbrOfVal; valNo++)
{
printf("Enter node value %d:", valNo+1);
scanf("%d", &val);
// Here we insert the value in both lists
lists= insertValue(lists, val);
globalList = insertValue(globalList, val);
}
start=addNodeBottom(val,lists);
if(listNo==0){
save=start;
}
printf("\n The list %d is: ",listNo+1);
display(lists);
}
printf("\n\n The final list is: ");
display(globalList);
printf("The first list is");
display(save);
printf("The second list is");
display(save->lsnext); //crashes here
return 0;
}
Node* insertValue(Node * list, int value) //to insert node at the end
{
Node *newNode, *m;
newNode = malloc(sizeof(Node));
newNode->number=value;
if(list == NULL)
{
newNode->next=NULL;
return newNode;
}
if(value < list->number)
{
newNode->next = list;
return newNode;
}
m = list;
while(m->next)
{
if(value < m->next->number)
break;
m = m->next;
}
newNode->next = m->next;
m->next = newNode;
return list;
}
Node* addNodeBottom(int val, Node *start)
{
Node*rear;
Node* node1=(Node*) malloc(sizeof(Node));
node1->number=val;
node1->lsnext=NULL;
if(start==NULL){
start=rear=node1;
}
else{
rear->lsnext=node1;
rear=node1;
}
return start;
}
void display(Node*nodex){
while(nodex)
{
printf("%d ->",nodex->number);
nodex=nodex->next;
}
}

Answer 1

This code invokes undefined behaviour. In particular, your function addNodeBottom is buggy: If invoked with start not NULL, it modifies the member rear->lsnext, but rear is uninitialised at that point. I assume, you intended to modify start instead. Here, you return start unmodified, so it's member lsnext is not set to anything useful, which probably eventually leads to a segmentation fault. However, in principle already the offending function call to addNodeBottom could lead to unexpected program termination.