动态建立链表

所谓动态链表是指在程序执行过程中从无到有地建立起一个链表，既一个一个地开辟结点和输入各结点的数据，并建立起前后相连的关系。

例题：
#include <iostream>
using namespace std;
#define NULL0    
struct student
{long num;
float score;
struct student *next;
};
int main()
{student a,b,c,*head,*p;
a.num=10001; a.score=89.5;
b.num=10003; b.score=90;
c.num=10007;c.score=85;    //为结点的num和score成员赋值
head=&a;                     //将结点a的起始地址赋给头指针head
a.next=&b;                   //将结点b的起始地址赋给a结点的next成员
b.next=&c;                   //将结点c的起始地址赋给b结点的next成员
c.next=NULL;                 //c结点的next成员不存放其他结点地址
p=head;                      //使p指针指向a结点
do       
  {cout<<p->num<<""<<p->score<<endl;//输出p指向的结点的数据
   p=p->next;                               //使p指向下一结点
  }while(p!=NULL);                         //输出完c结点后p的值为NULL
return 0;
}

1.针对例子写一个函数creat，用来建立一个动态链表。各结点的数据由键盘输入。

#include <iostream>
using namespace std;
#define NULL0    
struct student
{long num;
float score;
student *next;
};   
                   //定义n为全局变量，本文件模块中各函数均可使用它
student*creat(void)    //定义函数。此函数带回一个指向链表头的指针
{student *head;
student *p1,*p2;
int n=0;
p1=p2=newstudent;      //开辟一个新单元，并使p1,p2指向它
cin>>p1->num>>p1->score;
head=NULL;
while(p1->num!=0)
{n=n+1;
if(n==1) head=p1;
else p2->next=p1;
p2=p1;
p1=new student;
cin>>p1->num>>p1->score;
}
p2->next=NULL;
return(head);
}

2.写一个函数print，将上题建立的链表中各结点的数据依次输出。

#include <iostream>
using namespace std;
#define NULL0    
struct student
{long num;
float score;
student *next;
};   
intn;                   
void print(student *head)
{student *p;
cout<<"Now，These"<<n<<"records are："<<endl;
p=head;
if(head!=NULL)
do
   {cout<<p->num<<""<<p->score<<endl;
    p=p->next;
}while(p!=NULL);
}

3.写一个函数del，用来删除动态链表中的一个指定的结点（由实参指定某一学号，表示要删除该学生结点）。

#include <iostream>
using namespace std;
#define NULL0    
struct student
{long num;
float score;
student *next;
};   
intn;    
student *del(student *head,long num)
{student *p1,*p2;
if(head==NULL)                   //是空表
{cout<<"listnull!"<<endl; return(head);}
   p1=head;                         //使p1指向第一个结点
   while(num!=p1->num&& p1->next!=NULL)//p1指向的不是所要找的结点且后面还有结点
{p2=p1;p1=p1->next;}                //p1后移一个结点
if(num==p1->num)                       //找到了
{if(p1==head)head=p1->next;  //若p1指向的是首结点，把第二个结点地址赋予head
elsep2->next=p1->next;   //否则将下一结点地址赋给前一结点地址
cout<<"delete:"<<num<<endl;
n=n-1;
}
else cout<<"cannot find"<<num;    //找不到该结点
return(head);
}

4.写一个函数insert，用来向动态链表插入一个结点。

#include <iostream>
using namespace std;
#define NULL0    
struct student
{long num;
float score;
student*next;
};   
int n;  

student *insert(student *head,student *stud)
{student *p0,*p1,*p2;
p1=head;                         //使p1指向第一个结点
p0=stud;                         //指向要插入的结点
if(head==NULL)                   //原来的链表是空表
{head=p0;p0->next=NULL;}         //使p0指向的结点作为头结点
else
{while((p0->num>p1->num)&&(p1->next!=NULL))
{p2=p1;                      //使p2指向刚才p1指向的结点
p1=p1->next;}               //p1后移一个结点
if(p0->num<=p1->num)
{if(head==p1)head=p0;       //插到原来第一个结点之前
   elsep2->next=p0;           //插到p2指向的结点之后
  p0->next=p1;}
else
{p1->next=p0; p0->next=NULL;}}//插到最后的结点之后
  n=n+1;                             //结点数加１
   return (head);
}

5.将以上4个函数组成的程序，由主程序先后调用这些函数，实现链表的建立、输出、删除、和插入、在主程序中指定需要删除和插入的结点。
解一：
#include <iostream>
using namespace std;
#define NULL0    
struct student
{long num;
float score;
student *next;
};   
int n;

int main()
{ student *creat(void);
student *del(student *,long);
student *insert(student *,student *);
void print(student *);
student *head,*stu;
long del_num;
cout<<"inputrecords:"<<endl;
head=creat();                       //返回头指针
print(head);                         //输出全部结点
cout<<endl<<"inputthe deleted number:";
cin>>del_num;                       //输入要删除的学号
while(del_num!=0)
{head=del(head,del_num);             //删除后链表的头地址
  print(head);                        //输出全部结点
  cout<<"input the deletednumber:";
  cin>>del_num;
}
cout<<endl<<"inputthe inserted record:"; //输入要插入的结点
stu=newstudent;                     //开辟一个新结点
cin>>stu->num>>stu->score;
while(stu->num!=0)
{head=insert(head,stu);             //返回地址
  print(head);                        //输出全部结点
  cout<<endl<<"inputthe inserted record:"; //输入要插入的结点
   stu=new student;
  cin>>stu->num>>stu->score;
}
return 0;
}

student*creat(void)      //建立链表的函数
{student *head;
student *p1,*p2;
n=0;
p1=p2=newstudent;      //开辟一个新单元，并使p1,p2指向它
cin>>p1->num>>p1->score;
head=NULL;
while(p1->num!=0)
{n=n+1;
if(n==1) head=p1;
else p2->next=p1;
p2=p1;
p1=new student;
cin>>p1->num>>p1->score;
}
p2->next=NULL;
return(head);
}   

student *del(student *head,longnum)   //删除结点的函数
{student *p1,*p2;
if(head==NULL)                   //是空表
{cout<<"listnull!"<<endl; return(head);}
p1=head;                         //使p1指向第一个结点
while(num!=p1->num&& p1->next!=NULL)//p1指向的不是所要找的结点且后面还有结点
{p2=p1;p1=p1->next;}                //p1后移一个结点
if(num==p1->num)                       //找到了
{if(p1==head)head=p1->next;  //若p1指向的是首结点，把第二个结点地址赋予head
elsep2->next=p1->next;   //否则将下一结点地址赋给前一结点地址
cout<<"delete:"<<num<<endl;
n=n-1;
}
else cout<<"cannot find"<<num;    //找不到该结点
return(head);
}
   
student *insert(student *head,student *stud) //插入结点的函数
{student *p0,*p1,*p2;
p1=head;                         //使p1指向第一个结点
p0=stud;                         //指向要插入的结点
if(head==NULL)                   //原来的链表是空表
{head=p0;p0->next=NULL;}         //使p0指向的结点作为头结点
else
{while((p0->num>p1->num)&&(p1->next!=NULL))
{p2=p1;                      //使p2指向刚才p1指向的结点
p1=p1->next;}               //p1后移一个结点
if(p0->num<=p1->num)
{if(head==p1)head=p0;       //插到原来第一个结点之前
   elsep2->next=p0;           //插到p2指向的结点之后
  p0->next=p1;}
else
{p1->next=p0; p0->next=NULL;}}//插到最后的结点之后
  n=n+1;                        //结点数加１
   return (head);
}
              
void print(student*head)        //输出链表的函数
{student *p;
cout<<"Now，These"<<n<<"records are："<<endl;
p=head;
if(head!=NULL)
do
   {cout<<p->num<<""<<p->score<<endl;
    p=p->next;
}while(p!=NULL);
}
解二：
#include <iostream>
using namespace std;
#define NULL0    
struct student
{long num;
float score;
student *next;
};   
int n;

int main()
{ student *creat(void);
student *del(student *,long);
student *insert(student *,student *);
void print(student *);
student *head,stu;
long del_num;
cout<<"inputrecords:"<<endl;
head=creat();                       //返回头指针
print(head);                         //输出全部结点
cout<<endl<<"inputthe deleted number:";
cin>>del_num;                       //输入要删除的学号
head=del(head,del_num);             //删除后链表的头地址
print(head);                        //输出全部结点
cout<<endl<<"inputthe inserted record:"; //输入要插入的结点
cin>>stu.num>>stu.score;
head=insert(head,&stu);             //返回地址
print(head);                        //输出全部结点
cout<<endl<<"inputthe inserted record:"; //输入要插入的结点
cin>>stu.num>>stu.score;
head=insert(head,&stu);             //返回地址
print(head);
return 0;
}

student*creat(void)      //建立链表的函数
{student *head;
student *p1,*p2;
n=0;
p1=p2=newstudent;      //开辟一个新单元，并使p1,p2指向它
cin>>p1->num>>p1->score;
head=NULL;
while(p1->num!=0)
{n=n+1;
if(n==1) head=p1;
else p2->next=p1;
p2=p1;
p1=new student;
cin>>p1->num>>p1->score;
}
p2->next=NULL;
return(head);
}   

student *del(student *head,longnum)   //删除结的函数
{student *p1,*p2;
if(head==NULL)                   //是空表
{cout<<"listnull!"<<endl; return(head);}
p1=head;                         //使p1指向第一个结点
while(num!=p1->num&& p1->next!=NULL)//p1指向的不是所要找的结点且后面还有结点
{p2=p1;p1=p1->next;}                //p1后移一个结点
if(num==p1->num)                       //找到了
{if(p1==head)head=p1->next;  //若p1指向的是首结点，把第二个结点地址赋予head
elsep2->next=p1->next;   //否则将下一结点地址赋给前一结点地址
cout<<"delete:"<<num<<endl;
n=n-1;
}
else cout<<"cannot find"<<num;    //找不到该结点
return(head);
}
   
student *insert(student *head,student *stud) //插入结点的函数
{student *p0,*p1,*p2;
p1=head;                         //使p1指向第一个结点
p0=stud;                         //指向要插入的结点
if(head==NULL)                   //原来的链表是空表
{head=p0;p0->next=NULL;}         //使p0指向的结点作为头结点
else
{while((p0->num>p1->num)&&(p1->next!=NULL))
{p2=p1;                      //使p2指向刚才p１指向的结点
p1=p1->next;}               //p1后移一个结点
if(p0->num<=p1->num)
{if(head==p1)head=p0;       //插到原来第一个结点之前
   elsep2->next=p0;           //插到p2指向的结点之后*／
  p0->next=p1;}
else
{p1->next=p0; p0->next=NULL;}}//插到最后的结点之后
  n=n+1;                        //结点数加1
   return (head);
}
              
void print(student*head)        //输出链表的函数
{student *p;
cout<<"Now，These"<<n<<"records are："<<endl;
p=head;
if(head!=NULL)
do
   {cout<<p->num<<""<<p->score<<endl;
    p=p->next;
}while(p!=NULL);