设计一个函数 void add_poly(Polylist pa, Polylist pb) ，其功能是pb和pb的多项式进行相加。 

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#include <stdio.h>
#define NULL 0

//其中Polylist是如下结构体：
typedef struct Polynode {
	int coef;  //因子
	int exp;   //幂
	struct Polynode* next;
}Polynode, * Polylist;

//创建多项式的函数如下：
Polylist polycreate()
{
	Polynode* rear, * head, * s;

	int c, e;

	rear = head = (Polynode*)malloc(sizeof(Polynode));
	scanf("%d%d", &c, &e);
	while (c != 0)
	{
		s = (Polynode*)malloc(sizeof(Polynode));
		s->coef = c;
		s->exp = e;
		rear->next = s;
		rear = s;
		scanf("%d%d", &c, &e);
	}
	rear->next = NULL;
	return(head);
}

/*设计一个函数
void  add_poly(Polylist pa, Polylist pb)
其功能是pb和pb的多项式进行相加。*/
void add_poly(Polylist pa, Polylist pb)
{
	Polylist p, q, pre, temp;
	int sum;

	p = pa->next;
	q = pb->next;
	pre = pa;
	while (p && q)
	{
		if (p->exp < q->exp)
		{
			pre->next = p;
			pre = p;
			p = p->next;
		} 
		else if (p->exp > q->exp )
		{
			pre->next = q;
			pre = q;
			q = q->next;
		}
		else
		{
			sum = p->coef + q->coef;
			
			if (sum != 0)
			{
				pre->coef = sum;
				pre->next = q;
				pre = p;
				p = p->next;
			}
			else
			{
				temp = p;
				p = p->next;
				free(temp);
			}
			
			temp = q;
			q = q->next;
			free(temp);
		}
	}

	if (q != NULL)
	{
		pre->next = q;
	}
	else
	{
		pre->next = p;
	}

	free(pb);
}

//显示多项式的函数如下
void print(Polylist p)
{
	int j;

	p = p->next;
	while (p)
	{
		printf("%d", p->coef);
		for (j = 0; j < p->exp; j++)
			printf("*x");
		if (p->next != NULL)
			printf(" + ");
		p = p->next;
	}
	printf("\n");
}

//当执行如下的main函数后
void main(int argc, char* argv[])
{
	Polylist pa, pb;   //定义两个表示多项式的链表

	pa = polycreate();  //创建pa链表
	pb = polycreate();  //创建pb链表
	add_poly(pa, pb);   //做加法，结果保存在pa链表上
	print(pa);          //将加法的结果用一个多项式格式显示在输出设备上
}
/*
如果从键盘输入的值如下：
5 0
3 5
4 8
0 0
5 0
3 5
4 8
0 0

则执行的结果为
10 + 6 * x * x * x * x * x + 8 * x * x * x * x * x * x * x * x
*/