Program covering basics of linked list

#include<stdio.h>
#include<conio.h>
#include<alloc.h>
#include<iostream.h>
struct node
 {   int num;
      struct node *link;
 };
node *start , *save , *newptr , *ptr;
node * create_node ( int n )
{
      ptr  = ( node * )malloc(sizeof(struct node));
      ptr -> num = n;
      ptr -> link = NULL;
      return ptr;
}
void insert_node ( node *np , int n )
{
     node *tmp;
     if( start == NULL )
          start = np;
     else
     {    tmp = start;
          while (  tmp != NULL)
          { if ( tmp -> num <= n && ( tmp -> link -> num > n || tmp -> link == NULL))
                { np -> link = tmp -> link;
                   tmp -> link = np;
                   return;
                 }
            tmp = tmp -> link;
           }
      }
}
void del_beg()
{
         if ( start == NULL)
             printf("\nUnderflow");
        else
       {
             ptr = start;
             start = start -> link;
             free(ptr);
       }
}
void del (int inf)
{           ptr = start;
             node *tmp;
             while( ptr != NULL )
            {
                     if( ptr-> num == inf)
                    {        if ( ptr == start )
                              {    start = ptr ->link;
                                    free(ptr);
                                     return;
                              }
                             else
                             {      tmp = ptr;
                                     ptr = ptr->link;
                                     free(tmp);
                                     return;
                             }
                     }
                  else
                        ptr = ptr -> link;
              }
}
  void display ( node *np )
{
                 while (np != NULL )
                {     printf("%d" , np -> num );
                       printf("->>");
                       np = np -> link;
                 }
}
void main()
{
       clrscr();
       start = NULL ;
       int inf , ch1;
       char ch ;
       do
       {     printf("\n1.Insertion");
              printf("\n2.Deletion from begining");
              printf("\n3.Display");
              printf("\n4.Deletion of your choice");
              printf("\nEnter your choice:\t");
              scanf("%d" , &ch1 );
              switch(ch1)
             {    case 1:
                   printf("\nEnter the information of the new node:\t");
                   scanf("%d" , &inf );
                   printf("\nCreating new node!!! press Enter to continue");
                   getch();
                   newptr = create_node( inf ) ;
                   insert_node( newptr , inf );
                   display(start);
                   break;
                   case 2:
                   del_beg();
                    break;
                    case 3:
                    display(start);
                     break;
                    case 4:
                     printf("\nEnter the node to be delted:\t");
                     scanf( "%d" , inf );
                     del(inf);
                     break;
             }
              printf("\nDo you want to continue:\t");
              cin>>ch;
       }while ( ch == 'y' || ch == 'Y' );
       getch();
}