要求：
1  输入并建立多项式
2  输出多项式，输出形式外为整数序列：c1,e1;c2,e2;.......cn,en;其中n为多项式的项数，ci和ei分别为第i项的系数和指数，序列按指数降序排列
3  多项式a和b相加，建立多项式a+b
4  多项式a和b相减，建立多项式a-b
代码如下：
#include<stdio.h>
#include<malloc.h>
#define MAX 20  //多项式最多项数
typedef struct  //定义存放多项式的数组类型
{
  float coef;   //系数
  int exp;      //指数
}PolyArray[MAX];
typedef struct pnode  //定义单链表结点类型
{
  float coef;         //系数
  int exp;            //指数
  struct pnode *next;
}PolyNode;

void DispPoly(PolyNode *L)  //输出多项式
{
 PolyNode *p=L->next;
 while (p!=NULL)
 {
  printf("%g,%d;",p->coef,p->exp);
  p=p->next;
 }
 printf("\n");
}
void CreateListR(PolyNode * &L,PolyArray a,int n)    //尾插入法建表
{
 PolyNode *s,*r;int i;
 L=(PolyNode *)malloc(sizeof(PolyNode));          //创建头结点
 L->next=NULL;
// L->exp=n;
// printf("%d\n",L->exp);
 r=L;                                            //r始终指向终端结点，开始时指向头结点
  for(i=0;i<n;i++)
  {
    s=(PolyNode *)malloc(sizeof(PolyNode));   //创建新结点
    s->coef=a[i].coef;
    s->exp=a[i].exp;
    r->next=s;                               //将*s插入*r之后
    r=s;
  }
  r->next=NULL;                               //将终端结点next域置为NULL
}
void Sort(PolyNode * &head)                         //按exp域的值递减排序
{
  PolyNode *p=head->next,*q,*r;
  if(p!=NULL)                                      //当原单链表不为空时
  {
   r=p->next;                                     //r保存*p结点后继结点的指针
   p->next=NULL;                                  //构造只含一个数据结点的有序表
   p=r;
   while(p!=NULL)
   {
     r=p->next;                                   //r保存*p结点后继结点的指针
  q=head;
  while(q->next!=NULL && q->next->exp>p->exp)
   q=q->next;                               //在有序表中找插入*p的前驱结点*q
  p->next=q->next;                             //将*p插入到*q之后
  q->next=p;
  p=r;
   }
  }
}
void Add(PolyNode *ha,PolyNode *hb,PolyNode *&hc)//求两个有序表的并
{
  PolyNode *pa=ha->next,*pb=hb->next,*s,*tc;
  float c;
  hc=(PolyNode *)malloc(sizeof(PolyNode));           //创建头结点
  tc=hc;
  while(pa!=NULL && pb!=NULL)
  {
    if(pa->exp>pb->exp)
 {
   s=(PolyNode *)malloc(sizeof(PolyNode));        //复制结点
   s->exp=pa->exp;s->coef=pa->coef;
   tc->next=s;tc=s;
   pa=pa->next;
 }
 else if(pa->exp<pb->exp)
 {
  s=(PolyNode *)malloc(sizeof(PolyNode));           //复制结点
  s->exp=pb->exp;s->coef=pb->coef;
  tc->next=s;tc=s;
  pb=pb->next;
 }
 else                                             //pa->exp=pb->exp时
 {
 c=pa->coef+pb->coef;
 if(c!=0)                                          //系数之和不为0时创建新结点
 {
   s=(PolyNode *)malloc(sizeof(PolyNode));   
   s->exp=pa->exp;s->coef=c;
   tc->next=s;tc=s;
 }
 pa=pa->next;
 pb=pb->next;
 }

  }
  if(pb!=NULL)                                     //复制余下结点
   pa=pb;
  while(pa!=NULL)
  {
    s=(PolyNode *)malloc(sizeof(PolyNode));           //复制结点
 s->exp=pa->exp;s->coef=pa->coef;
 tc->next=s;tc=s;
 pa=pa->next;
  }
  tc->next=NULL;
}

void Subs(PolyNode *ha,PolyNode *hb,PolyNode *&hc)   //求两个有序表的差
{
  PolyNode *pa=ha->next,*pb=hb->next,*s,*tc;
  float c;
  hc=(PolyNode *)malloc(sizeof(PolyNode));           //创建头结点
  tc=hc;
  while(pa!=NULL && pb!=NULL)
  {
    if(pa->exp>pb->exp)
 {
   s=(PolyNode *)malloc(sizeof(PolyNode));        //复制结点
   s->exp=pa->exp;s->coef=pa->coef;
   tc->next=s;tc=s;
   pa=pa->next;
 }
 else if(pa->exp<pb->exp)
 {
  s=(PolyNode *)malloc(sizeof(PolyNode));           //复制结点
  s->exp=pb->exp;s->coef=-pb->coef;                 //如果前个多项式中的指数小于后个多项式指数加上负号
  tc->next=s;tc=s;
  pb=pb->next;
 }
 else                                             //pa->exp=pb->exp时
 {
 c=pa->coef-pb->coef;
 if(c!=0)                                          //系数之差不为0时创建新结点
 {
   s=(PolyNode *)malloc(sizeof(PolyNode));   
   s->exp=pa->exp;s->coef=c;
   tc->next=s;tc=s;
 }
 pa=pa->next;
 pb=pb->next;
 }

  }
  if(pb!=NULL)                                     //复制余下结点
   pa=pb;
  while(pa!=NULL)
  {
    s=(PolyNode *)malloc(sizeof(PolyNode));           //复制结点
 s->exp=pa->exp;s->coef=pa->coef;
 tc->next=s;tc=s;
 pa=pa->next;
  }
  tc->next=NULL;
}
void main()
{
   PolyNode *ha,*hb,*hc;
   //PolyArray a={{1.2,0},{2.5,1},{3.2,3},{-2.5,5}};
   //PolyArray b={{-1.2,0},{2.5,1},{3.2,3},{2.5,5},{5.4,10}};
   int m=4,n=5;
   PolyArray a,b;
   for(int i=0;i<m;i++)
   {
     printf("请输入A多项式中第%d项的系数和指数",i);
  scanf("%f%d",&a[i].coef,&a[i].exp);
   }
 
    for(int j=0;j<n;j++)
   {
     printf("请输入B多项式中第%d项的系数和指数",j);
  scanf("%f%d",&b[j].coef,&b[j].exp);
   }

   CreateListR(ha,a,4);
   CreateListR(hb,b,5);
   printf("原来A:\n");DispPoly(ha);
   printf("原来B:\n");DispPoly(hb);

   Sort(ha);
   Sort(hb);
   printf("排序后A:\n");DispPoly(ha);
   printf("排序后B:\n");DispPoly(hb);

   Add(ha,hb,hc);
   printf("相加后:\n");DispPoly(hc);
   Subs(ha,hb,hc);
   printf("相减后:\n");DispPoly(hc);
}