Garbage value for certain C functions - c

Question

I'm learning C and I'm trying to make a program with multiple linked list operations all at once. They don't give me errors, but for the functions to delete a node at the end, and to insert at a certain position, I'm getting a garbage value at the beginning of the output.
Temporary program to implement just the insert function:
#include <stdio.h>
#include <stdlib.h>
struct node
{
int data;
struct node* next;
};
void inp(struct node **start, int ele)
{
struct node *NEW = (struct node*)malloc(sizeof(struct node));
NEW->data = ele;
struct node *ptr = *start;
while(ptr != NULL)
{
if(ptr->next == NULL)
{
ptr->next = NEW;
NEW->next = NULL;
break;
}
ptr = ptr->next;
}
}
void insert_pos(struct node **start, int ele, int pos)
{
struct node *ptr = *start;
for(int i = 1; i < pos; i++)
{
ptr = ptr->next;
}
struct node *NEW = (struct node*)malloc(sizeof(struct node));
NEW->data = ele;
NEW->next = ptr->next;
ptr->next = NEW;
}
void display(struct node* start)
{
struct node* ptr = start;
while(ptr != NULL)
{
printf("%d\n", ptr->data);
ptr = ptr->next;
}
}
int main()
{
struct node *a;
int m;
for(int i = 0; i < 10; i++)
{
scanf("%d", &m);
inp(&a, m);
}
insert_pos(&a, 594, 3);
printf("\n\n");
display(a);
}
Temporary program to delete at the end:
//Temporary
#include <stdio.h>
#include <stdlib.h>
struct node
{
int data;
struct node* next;
};
void inp(struct node **start, int ele)
{
struct node *NEW = (struct node*)malloc(sizeof(struct node));
NEW->data = ele;
struct node *ptr = *start;
while(ptr != NULL)
{
if(ptr->next == NULL)
{
ptr->next = NEW;
NEW->next = NULL;
break;
}
ptr = ptr->next;
}
}
void del_end(struct node **start)
{
struct node *ptr = *start;
while(ptr != NULL)
{
if(ptr->next->next == NULL)
{
ptr->next = NULL;
free(ptr->next->next);
break;
}
ptr = ptr->next;
}
}
void display(struct node* start)
{
struct node* ptr = start;
while(ptr != NULL)
{
printf("%d\n", ptr->data);
ptr = ptr->next;
}
}
int main()
{
struct node *a;
int m;
for(int i = 0; i < 10; i++)
{
scanf("%d", &m);
inp(&a, m);
}
del_end(&a);
printf("\n\n");
display(a);
}
Any idea how to fix it?

Answer 1

you can see that in here:
The inp problem:
struct node *a;
puts a garbage value in a that you don't handle and uses it like a node,
add =NULL to solve.
also, your function that deletes from the end has the following error:
struct node *ptr = *start;
while(ptr != NULL)
{
if(ptr->next->next == NULL)
{
ptr->nexStack Overflow for Teams – Collaborate and share knowledge with a private group.t = NULL;
free(ptr->next->next);
break;
}
ptr = ptr->next;
}
you are changing ptr-> next and than accessing ptr->next->next...