调试没错，为什么运行时就有问题啊？到底是哪边有问题呢？
#include <iostream.h>
class ListNode
{
friend class List;


double value;

ListNode * next;

};

class List

{

int nCount;

ListNode * head;

public:

List() //无参构造函数

{nCount=0;
head=NULL;

}
~List() //析构函数

{
ListNode* p = head,*q;
while(p)
{
q = p->next;
delete p;
p = q;
}
}

List & operator = (List & l) //重载等号运算符

{ List l3;
nCount=l.nCount;

ListNode *f,*s;
int i;
s=l3.head;
f=l.head;
for(i=0;i<l.nCount;i++)
{l3.Add(f->value);
f=f->next;
}
head=s;
return l3;
}

void Add(double d) //添加一个元素

{ if (head == NULL)
{
head = new ListNode;
head->value = d;
head->next = NULL;
nCount++;
return;
}

ListNode *p,*q;
p=new ListNode;
p->next=NULL;
q=head;
while(q->next!=NULL)
{q=q->next;
}
q->next=p;
p->value=d;
nCount++;
}
void Remove(double d) //删除一个元素

{ ListNode *p;
if(head->value==d)
{
p = head;
head = head->next;
delete p;
nCount--;
return;
}

p=head->next;
ListNode *s=head;
while(p->value!=d)
{p=p->next;
s=s->next;
}
s->next=p->next;
delete(p);
nCount--;
}

void Print()

{

if( head==NULL) return;

cout << "LIST(" << nCount <<") =" << head->value;

ListNode * p=head->next;

while(p!=NULL)

{

cout << ", "<< p->value;

p=p->next;

}

cout <<endl;

}

};





void main()
{
List list1;
double d;
int n;
cin >>n;
while (n>0)
{
cin >>d;
list1.Add(d);
n--;
}
list1.Print();
List list2;
list2.Add(2.4);
list2.Add(6.1);
list2.Print();
list2=list1;
cin >>d;
list2.Remove(d);
cin >>d;
list2.Remove(d);
list2.Print();
}


[解决办法]
你的代码修改如下：

C/C++ code

#include <iostream>using namespace std;class ListNode{  friend class List;  double value;  ListNode * next;};class List{  int nCount;  ListNode * head;public:  List() //无参构造函数  {nCount=0;  head=NULL;  }  ~List() //析构函数  {  ListNode* p = head,*q;  while(p)  {  q = p->next;  delete p;  p = q;  }  }  List & operator = (List & l) //重载等号运算符  {       if(this->head == l.head)          return *this;  ListNode *f,*s;  s = head;    while(head)      {          s = s->next;          delete head;          head = s;      }    nCount = 0;int i;f=l.head;for(i=0;i<l.nCount;i++){Add(f->value);f=f->next;}  return *this;  }  void Add(double d) //添加一个元素  { if (head == NULL)  {  head = new ListNode;  head->value = d;  head->next = NULL;  ++nCount;  return;  }  ListNode *p,*q;  p=new ListNode;  p->next=NULL;  q=head;  while(q->next!=NULL)  {q=q->next;  }  q->next=p;  p->value=d;  ++nCount;  } void Remove(double d) //删除一个元素  { ListNode *p;  if(head->value==d)  {  p = head;  head = head->next;  delete p;nCount--;  return;  }  p=head->next;  ListNode *s=head;  while(p &&p->value!=d)  {p=p->next;  s=s->next;  }  if(p == NULL)      return;  s->next=p->next;  delete(p);  nCount--;  }  void Print()  {  if( head==NULL) return;  cout << "LIST(" << nCount <<") =" << head->value;  ListNode * p=head->next;  while(p!=NULL)  {  cout << ", "<< p->value;  p=p->next;  }  cout <<endl;  }};int main(){List list1; double d; int n; cin >>n; while (n>0) {  cin >>d;  list1.Add(d);  n--; } list1.Print(); List list2; list2.Add(2.4); list2.Add(6.1); list2.Print(); list2=list1; cin >>d; list2.Remove(d); cin >>d; list2.Remove(d); list2.Print();return 0;}