数据结构C++第一个实验作业，用顺序表完成的两个一元多项式加减法。

#include 
using namespace std;
#define MAXSIZE 101
typedef struct {
	float coef; //系数
	int expn;  //指数
}Polynomial;


typedef struct {
	Polynomial* elem;
	int length;
}SqList;


void seletSort(SqList& L) {  //选择排序
	Polynomial temp;
	for (int i = 1; i < L.length; i++) {
		for (int j = i + 1; j <= L.length; j++) {
			if (L.elem[i].expn < L.elem[j].expn) {
				temp = L.elem[j];
				L.elem[j] = L.elem[i];
				L.elem[i] = temp;
			}
		}
	}
}

void InitList(SqList &L) {
	L.elem = new Polynomial[MAXSIZE];
	if (!L.elem)exit(1);
	L.length = 0;
}

void assignList(SqList& L) {   //赋值操作
	InitList(L);
	int i = 1;  //9 2 6 7 6 5 4 3 1 4 5 9 2 1 0 0
		        //5 6 2 9 -9 3 1 0 5 1 -7 2 -10 4 0 0          
	cout << "请输入多项式系数和幂次,分别输入两个0结束读入" << endl;
	while (1){
		cout << "第" << i << "项:";
		cin >> L.elem[i].coef;
		cin >> L.elem[i].expn;
		if (L.elem[i].coef == 0 && L.elem[i].expn == 0)break;
		i++;
		L.length++;
	}
	seletSort(L);
	cout << "赋值完成" << endl;
}
void print(SqList L) {
	for (int i = 1; i <= L.length; i++) {   //if判断当系数为0、1，幂次为0、1的特殊情况
		if (L.elem[i].coef == 0)continue;//系数为0
		if(L.elem[i].expn==0)cout << L.elem[i].coef ;//幂次为0
		else if (L.elem[i].expn == 1&& L.elem[i].coef == 1)cout << "X" ;//幂次系数均为1
		else if (L.elem[i].expn == 1)cout << L.elem[i].coef << "X" ;//幂次为1
		else cout << L.elem[i].coef << "X^" << L.elem[i].expn ;
		if (i != L.length&& L.elem[i+1].coef>0)cout << '+'; //后面的系数为负数最后一项没有加号	
	}
	cout << endl;
}

void addPloy(SqList L1,SqList L2,SqList& L3) {
	L3.elem = new Polynomial[2 * MAXSIZE];
	int i = 1, j = 1,k = 1;
	while (i <= L1.length && j <= L2.length) {
		if (L1.elem[i].expn > L2.elem[j].expn) {
			L3.elem[k] = L1.elem[i];
			i++; k++;
		}
		else if(L1.elem[i].expn < L2.elem[j].expn) {
			L3.elem[k] = L2.elem[j];
			j++; k++;
		}
		else {   //合并同类项
			L3.elem[k].coef = L2.elem[j].coef+ L1.elem[i].coef;
			L3.elem[k].expn = L2.elem[j].expn;
			i++; j++; k++;
		}
	}
	if (i > L1.length) {
		while (j <= L2.length) {
			L3.elem[k] = L2.elem[j];
			j++; k++;
		}
	}
	else {
		while (i <= L1.length) {
			L3.elem[k] = L1.elem[i];
			i++; k++;
		}
	}
	L3.length=k-1;
}

void transformInverse(SqList& L) {  //各项系数转换为相反数
	for (int i = 1; i <= L.length; i++) {
		L.elem[i].coef = -L.elem[i].coef;
	}
}

void minusPloy(SqList L1, SqList& L2, SqList& L3) {
	transformInverse(L2);//被减式子系数全部转为相反数再相加
	addPloy(L1, L2, L3);
}

int main() {
	SqList P1,P2,P3;
	int n;
	cout << "输入1两式相加,输入2两式相减"<> n;
	switch (n)
	{
	case 1:
		cout << "输入第一个式:" << endl;
		assignList(P1);
		print(P1);
		cout << "输入第二个式:" << endl;
		assignList(P2);
		print(P2);
		cout << "完成相加操作:" << endl;
		addPloy(P1, P2, P3);
		print(P3);
		break;
	case 2:
		cout << "输入减式:" << endl;
		assignList(P1);
		print(P1);
		cout << "输入被减式:" << endl;
		assignList(P2);
		print(P2);
		cout << "完成相减操作:" << endl;
		minusPloy(P1, P2, P3);
		print(P3);
		break;
	default:
		cout << "非法输入" << endl;
		break;
	}
	return 0;
}