为什么（delete pheap;   pheap=new int;）两个或其中的一个可去可不去，两种情况执行结果一样。
#include<iostream.h>
int main()
{
 int localvariable=5;
 int *plocal=&localvariable;
 int *pheap=new int;
 *pheap=7;
 cout<<"localvariable:"<<localvariable<<endl;
 cout<<"*plocal:"<<*plocal<<endl;
 cout<<"*pheap:"<<*pheap<<endl;
 delete pheap;
 pheap=new int;
 *pheap=9;
 cout<<"*pheap:"<<*pheap<<endl;
 delete pheap;
 return 0;
}