#include<iostream>
using namespace std;
typedef struct LNode{
       int   data;
       struct LNode *next;
}LNode;
      
void createlist_L(LNode *L,int n)
{
     //逆序输入N个元素的值，建立带表头结点的单链表L
     LNode *p;
     int i;
     L=(LNode *)malloc(sizeof(LNode));
     L->next = NULL;//先建立一个带头结点的单链表
     for(i=n;i>0;--i)
     {
          p=(LNode *)malloc(sizeof(LNode));//生成新结点
          scanf("%d",&p->data);
          p->next = L->next;//插入到表头
          L->next = p;
     }
}//creatlist L
void insert(LNode *L,LNode *q)
{
     LNode *p;
     p=(LNode *)malloc(sizeof(LNode));
     p->data=q->data;
     p->next=L->next;
     L->next=p;
   
   
}//插入某 一元素
void Mergelist_L(LNode *La,LNode *Lb){
     //已知的单链表La和Lb的元素按值非递减排列
     //归并La和Lb得到新的单链表Lc，Lc的元素也按值非递减排列。
     LNode *pa,*pb;
     Lc=(LNode *)malloc(sizeof(LNode));
     
     Lc->next=NULL;
     pa=La->next; pb=Lb->next;  
     while(pa && pb)
     {
           if(pa->data < pb->data)
           {
                insert(Lc,pa); pa=pa->next;
           }
           else if(pa->data > pb->data)
           {insert(Lc,pb); pb=pb->next;}
           else {insert(Lc,pa); pa=pa->next; pb=pb->next;}  
     }
   
          while(pa)
          {insert(Lc,pa);  pa=pa->next;}
          while(pb)
          {insert(Lc,pb); pb=pb->next;}//将剩余段插入Lc中
     while(Lc->next!=NULL)
     {
           Lc=Lc->next;
           cout <<Lc->data << " ";
     }
     cout << endl;
}
int main(){

     LNode *La,*Lb,*Lc;
     int a,b;
     cout <<"请输入A链表中元素的数目";
     cin >> a;
     cout <<"请按非递增顺序输入A链表中的元素";
     createlist_L(La,a);
     cout <<"请输入B链表中元素的数目";
     cin >> b;
     cout <<"请按非递增顺序输入B链表中的元素";
     createlist_L(Lb,b);
     cout <<"AUB  ";  Mergelist_L(La,Lb);
     return 0;
}

为什么不能调用一个插入函数呢

while(pa && pb)
      {
            if(pa->data < pb->data)
            {
                pc->next=pa;
                pa=pa->next;
                pc=pc->next;
            }
            else if(pa->data > pb->data)
            {
                pc->next=pb;
                pb=pb->next;
                pc=pc->next;
            }
            else
            {
                 pc->next=pa;
                 pa=pa->next;
                 pb=pb->next;
                 pc=pc->next;
            }
      }
      while(pa)      
      {
          pc->next=pa;
          pa=pa->next;
          pc=pc->next;
      }
      while(pb)
      {
          pc->next=pb;
          pb=pb->next;
          pc=pc->next;
      }//将剩余段插入Lc中
      pc->next=NULL;
      while(Lc->next!=NULL)
      {
            Lc=Lc->next;
            cout <<Lc->data << " ";
      }
      cout << endl;
楼上的大哥，我想输出数学意义上的并集，将代码修改如上，可是运行结果不完全正确，La中的数好像读不到最后

太好了，错误解决了，不过我还是得好好想一下，谢谢啊！