代码本是用来解决在一个链表中插入一个元素，但是运行后结果总是与本意不同。亲们帮帮忙，看看怎么错了。

#include
using namespace std;
struct List //定义一个结构体表示线性表
{
int num;
struct List *next;
};
int main()
{
List la,*p,*head,*p1,*pm; //定义线性表la

                                           //把表a的首元素地址赋给p和head
int n=1,m,t;
cout<<"请输入表a中的第"<<1<<"个元素"<<endl;
cin>>la.num;
p=&la;head=&la;p1=&la;
cout<<"是否继续输入,继续就输入1，不继续就输入0"<<endl;
cin>>t;
if(t!=1&&t!=0)
{
    cout<<"输入错误，请重新输入"<<endl;
    cout<<"是否继续输入,继续就输入1，不继续就输入0"<<endl;
    cin>>t;
}
if(t)
do
{
    p->next =new List;
    p=p->next ;
    cout<<"请输入表a中的第"<<n+1<<"个元素"<<endl;
    cin>>p->num;
    cout<<"是否继续输入,继续就输入1，不继续就输入0"<<endl;
    cin>>t;
    if(t!=1&&t!=0)
    {
        cout<<"输入错误，请重新输入"<<endl;
        cout<<"是否继续输入,继续就输入1，不继续就输入0"<<endl;
        cin>>t;
    }
    n++;
}while(t);
p->next =new List;
p=head;
cout<<"总共有"<<n<<"个元素"<<endl;
cout<<"表中元素为"<<endl;
for(int i=1;i<=n;i++)
{
    cout<<p->num <<" ";
    p=p->next;
}
p=head;
cout<<"表a中的元素已经输入完成，请输入要插入新元素的位置数m"<<endl;
cin>>m;
pm=new List;
cout<<"输入要插入的新元素"<<endl;
cin>>pm->num;
pm->next =p+m;
(p+m-1)->next =pm ;
cout<<p->num <<' '<<(p+m-1)->num <<' '<<pm->num<<endl;
for(int j=1;j<=n;j++)
{
    cout<<p1->num<<' ';
    p1=p1->next;
}
return 0;

}

    1 #include <iostream>
    2 using namespace std;
    3 struct List //露篓?一赂枚鹿?卤铆??卤铆
    4 {
    5     int num;
    6     struct List *next;
    7 };
    8 int main()
    9 {
 10     List la,*p,*head,*p1,*pm; //露篓???卤铆
 11                                                //掳驯铆??陋?碌?路赂鲁赂酶ead
 12     int n=1,m,t;
 13     cout<<"input "<<1<<"item"<<endl;
 14     cin>>la.num;
 15     p=&la;head=&la;p1=&la;
 16 
 17     cout<<"1 go on, 0 terminal"<<endl;
 18     cin>>t;
 19     if(t!=1&&t!=0)
 20     {
 21         cout<<"err, try again:"<<endl;
 22         cout<<"1 go on, 0 terminal"<<endl;
 23         cin>>t;
 24     }
 25 
 26     if(t)
 27     {
 28         do
 29         {
 30             p->next =new List;
 31             p=p->next ;
 32             cout<<"input"<<n+1<<"item"<<endl;
 33             cin>>p->num;
 34             cout<<"1 go on, 0 terminal"<<endl;
 35             cin>>t;
 36             if(t!=1&&t!=0)
 37             {
 38                 cout<<"err, try again:"<<endl;
 39                 cout<<"1 go on, 0 terminal"<<endl;
 40                 cin>>t;
 41             }
 42             n++;
 43         }while(t);
 44 
 45         // p->next =new List;
 46 
 47         p=head;
 48         cout<<"total"<<n<<"item"<<endl;
 49         cout<<"contents:"<<endl;
 50         for(int i=1;i<=n;i++)
 51         {
 52             cout<<p->num <<" ";
 53             p=p->next;
 54         }
 55         p=head;
 56         cout<<"insert m"<<endl;
 57         cin>>m;
 58         pm=new List;
 59         cout<<"insert num"<<endl;
 60         cin>>pm->num;
 61         // pm->next =p+m;
 62         // (p+m-1)->next =pm ;
 63         struct List *pre = p;
 64         struct List *cur = p;
 65         for( int i = 0; i <= m; i++ )
 66         {
 67             if( i == m )
 68             {
 69                 pm->next = cur;
 70                 pre->next = pm;
 71             }
 72             pre = cur;
 73             cur = cur->next;
 74         }
 75 
 76         n++;      // ?要录?
 77         cout<<p->num <<' '<<(p+m-1)->num <<' '<<pm->num<<endl;
 78 
 79         for(int j=1;j<=n;j++)
 80         {
 81             cout<<p1->num<<' ';
 82             p1=p1->next;
 83         }
 84     }
 85     return 0;
 86 }