在 C++ 中删除指针

I've seen quite a few questions over in SO about deleting pointers but they all seem to be related to deleting a class and not a 'simple' pointer (or whatever the proper term might be), here's the code I'm trying to run:

#include <iostream>;

using namespace std;

int main() {
  int myVar,
      *myPointer;

  myVar = 8;
  myPointer = &myVar;

  cout << "delete-ing pointers " << endl;
  cout << "Memory address: " << myPointer << endl;

  // Seems I can't *just* delete it, as it triggers an error 
  delete myPointer;
  cout << "myPointer: " << myPointer << endl;
  // Error: a.out(14399) malloc: *** error for object 0x7fff61e537f4:
  // pointer being freed was not allocated
  // *** set a breakpoint in malloc_error_break to debug
  // Abort trap: 6

  // Using the new keyword befor deleting it works, but
  // does it really frees up the space? 
  myPointer = new int;
  delete myPointer;
  cout << "myPointer: " << myPointer << endl;
  // myPointer continues to store a memory address.

  // Using NULL before deleting it, seems to work. 
  myPointer = NULL;
  delete myPointer;
  cout << "myPointer: " << myPointer << endl;
  // myPointer returns 0.

}

所以我的问题是:

1. 为什么第一个案例不起作用?使用和删除指针似乎是最直接的用法?该错误表示内存未分配，但cout"返回了一个地址.
2. 在第二个示例中，错误不是被触发，而是对 myPointer 的值进行计算 仍然 返回内存地址?
3. #3 真的有效吗?似乎对我有用，指针不再存储地址，这是删除指针的正确方法吗?

抱歉问了这么长的问题，想尽可能清楚地说明这一点，还要重申一下，我的编程经验很少，所以如果有人能用外行的术语回答这个问题，将不胜感激！

myVar = 8; //not dynamically allocated. Can't call delete on it.
myPointer = new int; //dynamically allocated, can call delete on it.

  myPointer = NULL;
  delete myPointer;

myPointer = new int;
myPointer = NULL; //leaked memory, no pointer to above int
delete myPointer; //no point at all

myPointer = new int;
delete myPointer; //freed memory
myPointer = NULL; //pointed dangling ptr to NULL