Implementation of Singly Linked List (C++)
struct Node would benefit from its own constructor. As a side note, if you don't want to expose struct Node to the client (and trust me, you don't), better make it private to class LinkedList.

tmp doesn't deserve to be a class member. It is strictly local to each method.

DRY. push_back could and should be streamlined:
  struct Node * tmp = new Node(data);
  if (begin) {
      last-&gt;next = tmp;
  } else {
      begin = tmp;
  }
  last = tmp;


display_all should not print anything on the empty list. The caller might be greatly confused.

clear could and should be streamlined. Run the loop till nullptr:
  while (begin) {
      struct Node * tmp = begin-&gt;next;
      delete begin;
      begin = tmp;
  }
  last = nullptr;

As a side note, prefer nullptr to NULL.