双链表改错!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 哥们我非要把指针弄明白!

[zhengviolet]

#include <iostream>
using namespace std;
struct Node
{
int data;
Node *left,*right;
};
class Dlist
{
public:
Dlist()
{
head=NULL;
};
void Create();
void Find();
void Display();
void Insert();
void Delete();
private:
Node *head;
};
void Dlist::Create()
{
int x;
head = new Node;
Node *p = head;
bool cycle=true;
cout<< "please input num:"<<endl;
while(cycle)
{
cin>>x;
if(x!=0)
{
Node *s = new Node;
s->data = x;
p->right = s;
s->left = p;
p=s;
}
else
cycle = false;
}
p = head;
head = head->right;
head->left = NULL;
p->right = NULL;
delete p;
}
void Dlist::Display()
{
Node *p = head;
while ( p != NULL )
{
cout <<" "<<p->data;
p=p->right;
}
cout <<endl;
delete p;
}
void Dlist::Find()
{
Node *p = head;
int x;
cout << "please input you want find num: "<<endl;
cin >>x;
while ( p != NULL && p->data != x )
p=p->right;
if( p != NULL )
cout << "find !"<<endl;
else
cout <<" no find! "<<endl;
delete p;

}
void Dlist::Insert()
{
int position ,num ,i = 1;
Node *p = NULL;
Node *s = new Node;
cout <<"please input insert position: "<<endl;
cin >>position;
cout <<"please input insert num: "<<endl;
cin >>num;
s->data = num;
if ( position == 0 )
{
s->right=head;
head->left = s;
head = s;
head->left = NULL;
}
else
{
p = head;
while ( p != NULL && i < position-1 )
{
p = p->right;
i++;
}
if ( p != NULL )
{
if ( p->right == NULL )
{
p->right = s;
s->left = p;
s->right = NULL;
}
else
{
s->right = p->right;
p->right->left = s;
p->right = s;
s->left = p;
}
cout << "insert success!"<<endl;
}
else
cout << "insert failed!"<<endl;

}
}
void Dlist::Delete()
{
int num;
Node *p = NULL;
Node *q = NULL;
cout << "please input delete num:"<<endl;
cin >>num;
if ( head == NULL )
cout << "the list overflow!"<<endl;
if ( head->data == num )
{
p = head;
head = head->right;
head->left = NULL;
cout << "the num was delete at head!"<<endl;
}
else
{
q = head;
p = head->right;
while ( p != NULL && p->data != num )
{
q = p;
p = p->right ;
}
if ( p != NULL )
{
if ( p->right == NULL )
{
p->left->right = NULL;
delete p;
}
else
{
p->left->right = p->right;
p->right->left = p->left;
delete p;
}
cout << "the num was delete!"<<endl;
}
else
cout <<" not find num !"<<endl;
}
}
void main()
{
Dlist DL;
DL.Create();
DL.Display();
DL.Find();
DL.Display();
DL.Insert();
DL.Display();
DL.Delete();
DL.Display();
}
不知道是哪错了!请教!

[phidix]

很多错，包括Create()里。手头只有一个当初给别人写的单链表的小程序，可参考一下。

动态建立一个带头结点的单链表A，元素由键盘输入，将A分解为两个带头
结点的单链表A和B，使得A中含有原表中序号为奇数的元素，而B表中含有原表
中序号为偶数的元素，且保持其相对顺序，完成操作后，分别输出显示A,B表中
元素

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <malloc.h>

typedef struct Nodetag
{
int Val;
struct Nodetag * pNext;
}Node;

/*add a node at tail*/
void AddNode(Node ** ppHead,int nVal)
{
Node * pNode;
pNode = *ppHead;
if(pNode==NULL)
{
pNode = (Node *)malloc(sizeof(Node));
if(pNode==NULL)
{
printf("\nOut of memory!");
exit(0);
}
pNode->pNext = NULL;
pNode->Val = nVal;
*ppHead = pNode;
}
else
{
while(1)
{//seek to end of train
if(pNode->pNext!=NULL)
{
pNode = pNode->pNext;
continue;
}
else
{
break;
}
}
pNode->pNext = (Node *)malloc(sizeof(Node));
if(pNode->pNext==NULL)
{
printf("\nOut of memory!");
exit(0);
}
pNode->pNext->pNext = NULL;
pNode->pNext->Val = nVal;
}
return;
}

/*
the very main funciton,the entrance of the application
*/
int main(int argc, char* argv[])
{
Node * pTrainA;
Node * pTrainB;
Node * pNode;
Node * pTemp;
int nVal;
int temp;
pTrainA = NULL;
pTrainB = NULL;
pNode = NULL;
pTemp = NULL;

printf("\n\n---Train test---");
printf("\nNow input interges,one at a time.Input ^Z to end array.\n");
while(1)
{
printf("New element:");
temp = scanf("%d",&nVal);
if(temp == 0)
{/*invalid input*/
printf("Invalid input!\n");
fflush(stdin);
continue;
}
else if(temp == -1)
{/*^Z got,break out.*/
break;
}
else
{/*add new node*/
AddNode(&pTrainA,nVal);
}
}
printf("Input end!");

/*show train A*/
printf("\n\nTrainA: ");
pNode = pTrainA;
if(pNode==NULL)
{
printf("Empty!");
}
while(pNode!=NULL)
{
printf("%d",pNode->Val);
if(pNode->pNext!=NULL)
{
printf(",");
}
pNode = pNode->pNext;
}

printf("\n\nConverting...");
pNode = pTrainA;
while(pNode!=NULL)
{
if(pNode->pNext!=NULL)
{
AddNode(&pTrainB,pNode->pNext->Val);
pTemp = pNode->pNext;
pNode->pNext = pNode->pNext->pNext;
delete pTemp;
}
pNode = pNode->pNext;
}
printf("OK!");

/*show train A*/
printf("\n\nTrainA: ");
pNode = pTrainA;
if(pNode==NULL)
{
printf("Empty!");
}
while(pNode!=NULL)
{
printf("%d",pNode->Val);
if(pNode->pNext!=NULL)
{
printf(",");
}
pNode = pNode->pNext;
}

/*show train B*/
printf("\nTrainB: ");
pNode = pTrainB;
if(pNode==NULL)
{
printf("Empty!");
}
while(pNode!=NULL)
{
printf("%d",pNode->Val);
if(pNode->pNext!=NULL)
{
printf(",");
}
pNode = pNode->pNext;
}

printf("\n\nThe End.Press any key to continue...");
while(1)
{
if(_kbhit())
{
break;
}
}
return 0;
}

[yaozijian110]

这是我改好的程序，你看看
我是用VC实验的，所以iostream变成了iostream.h，去掉了namespace
改了的地方我都标了出来。有几个地方其实是对的，但是不太简洁，我也改了一下。


#include <iostream.h>

struct Node
{
int data;
Node *left,*right;
};
class Dlist
{
public:
Dlist()
{
head = NULL;
};
void Create();
void Find();
void Display();
void Insert();
void Delete();

private:
Node *head;
};

void Dlist::Create()
{
int x;
head = new Node;
Node *p = head;
bool cycle = true;

cout<< "please input num:"<<endl;
while(cycle)
{
cin>>x;
if(x!=0)
{
Node *s = new Node;
s->data = x;
p->right = s;
s->left = p;
p=s;
}
else
cycle = false;
}
//******************
p->right = NULL;
//******************
p = head;
head = head->right;
head->left = NULL;
p->right = NULL;
delete p;
}

void Dlist::Display()
{
Node *p = head;
while ( p != NULL )
{
cout <<" "<<p->data;
p = p->right;
}
cout <<endl;
//delete p;
}

void Dlist::Find()
{
Node *p = head;
int x;
cout << "please input you want find num: "<<endl;
cin >>x;
while ( p != NULL && p->data != x )
p=p->right;
if( p != NULL )
cout << "find !"<<endl;
else
cout <<" no find! "<<endl;
//delete p;

}
void Dlist::Insert()
{
int position ,num ,i = 1;
Node *p = NULL;
Node *s = new Node;

cout <<"please input insert position: "<<endl;
cin >>position;
cout <<"please input insert num: "<<endl;
cin >>num;

s->data = num;
if ( position == 0 )
{
s->right=head;
head->left = s;
head = s;
head->left = NULL;
}
else
{
p = head;
//while ( p != NULL && i < position - 1 )
while ( p != NULL && i < position )
{
p = p->right;
i++;
}
if ( p != NULL )
{
if ( p->right == NULL )
{
p->right = s;
s->left = p;
s->right = NULL;
}
else
{
s->right = p->right;
p->right->left = s;
p->right = s;
s->left = p;
}
cout << "insert success!"<<endl;
}
else
cout << "insert failed!"<<endl;

}
}
void Dlist::Delete()
{
int num;
Node *p = NULL;
Node *q = NULL;
cout << "please input delete num:"<<endl;
cin >>num;
if ( head == NULL )
cout << "the list overflow!"<<endl;
if ( head->data == num )
{
p = head;
head = head->right;
head->left = NULL;
cout << "the num was delete at head!"<<endl;
//**************
delete p;
//**************
}
else
{
q = head;
p = head->right;
while ( p != NULL && p->data != num )
{
q = p;
p = p->right ;
}
if ( p != NULL )
{
if ( p->right == NULL )
{
//p->left->right = NULL;
q->right = NULL;
delete p;
}
else
{
//p->left->right = p->right;
q->right = p->right;

//p->right->left = p->left;
p->right->left = q;
delete p;
}
cout << "the num was delete!"<<endl;
}
else
cout <<" not find num !"<<endl;
}
}
void main()
{
Dlist DL;

DL.Create();
DL.Display();
DL.Find();
DL.Display();
DL.Insert();
DL.Display();
DL.Delete();
DL.Display();
}

[yaozijian110]

刚才忘了，Dlist类最好还加一个如下的析构函数，否则会有内存泄漏的。

~Dlist()
{
Node *p = head;
while (p)
{
head = p->right;
delete p;
p = head;
}
}

[sisijin]

同意楼上的观点，主要的问题在于链表尾结点的right指针未赋初值，因此是未定义的，那么在display或者find之类的函数中通过while ( p != NULL )形式的判断得不到正确的结果。我比较喜欢用的方法是给这个结构体写一个构造函数：
struct Node
{
int data;
Node *left,*right;
struct Node(){ left = right = NULL;}
};
这样就不用担心忘记给指针赋初值而引起的指针指向错误了:)

[zhengviolet]

问题已经找到，就是楼上的这位大哥改的一个地方
p = head;
head = head->right;
head->left = NULL;
p->right = NULL;
应该改为：p->right = NULL;
p = head;
head = head->right;
head->left = NULL;
就是顺序变一下!
但下面的其它地方改不改结果都正确，WHY？

[wwwooowww]

type struct
{
int data;
Node *left,*right;
}Node;

[falcon1210]

你应该先说哪个函数错了

[zhengviolet]

我不知道哪个函数错了呀!Create()应该没有错，Display()一定错了!
Find()也错了!但都不知道错哪了呀？