7-2 一元多项式的乘法与加法运算 (20分)

int a[1005], b[1005], c[2005], d[1005];

int main() {
	//输入第一个多项式 
	int n1; cin >> n1;
	for(int i = 0; i < n1; i ++) {
		int x, y;
		cin >> x >> y;
		a[y] = x;
	}
	//输入第二个多项式 
	int n2; cin >> n2;
	for(int i = 0; i < n2; i ++) {
		int x, y;
		cin >> x >> y;
		b[y] = x;
	}
	
	//多项式相乘 
	for(int i = 0; i <= 1000; i ++) {
		if(a[i]) {
			for(int j = 0; j <= 1000; j ++) {
				if(b[j]) {
					c[i + j] += a[i] * b[j]; //+= 
				}
			}
		}
	}
	bool f = 0;
	for(int i = 2000; i >= 0; i --) {
		if(c[i]) {
			if(f) cout << " ";
			cout << c[i] << " " << i;
			f = 1;
		}
	}
	if(f == 0) cout << "0 0";
	cout << endl;
	
	//多项式相加 
	for(int i = 0; i <= 1000; i ++) {
		d[i] = a[i] + b[i];
	}
	f = 0;
	for(int i = 1000; i >= 0; i --) {
		if(d[i]) {
			if(f) cout << " ";
			cout << d[i] << " " << i;
			f = 1;
		}
	}
	if(f == 0) cout << "0 0";
	
	return 0;
}

多项式相乘时要用+=赋值，合并同类项