Thread: Problem in link list

Hi,

I have create a simple program for displaying a link list,but it is not working properly.
The code is as follow:

Code:

#include<stdio.h>
#include<stdlib.h>

struct linklist
{
 int data;
 struct linklist *next;
};
struct linklist *ptr;

void insert(linklist *ptr)
{
    printf("INSIDE INSERT%u",ptr );
    int num; 
    struct linklist *temp = ptr;
    struct linklist *node = (struct linklist *)malloc(sizeof(struct linklist));
    printf("\n Enter the data \n");
    scanf("%d",&num);
    node->data = num;

    if ( ptr == NULL ) {
        printf("INSIDE IF%u",ptr );
        ptr = node;
        node->next = NULL;
    }
    else {
        printf("INSIDE ELSE"); 
        while ( temp->next != NULL ) {
            temp = temp->next;
        }
        temp->next = node;
        node->next = NULL;
       }
}

void display(linklist *ptr) 
{
    struct linklist *temp = ptr;
    while ( temp != NULL ) {
        printf("%d",temp->data );
        temp = temp->next; 
    }
}

    
int main()
{
 ptr = NULL; 
    int ch;
    while ( 1 ) {

      switch ( ch ) {
      
          case 1:
          insert(ptr);
          break;
 
          case 2:
          display(ptr);
          break;
  
          case 3:
          exit(0);
      }

   printf("\nEnter your choice ");
   scanf("%d",&ch);
  }
}

The problem is that in insert(ptr) function it always showing the ptr value 0 i.e NULL which I don't understand since the ptr I have declared as global so it should not be initialized to 0 every time the loop runs.
Can anybody explain me the behavior and solution to it.

Thanks

ptr should be allocated first...