如何用C++算圆数据

最近上到了圆这一单元，我这么懒的人就直接写代码了

废话不多说，直接上代码

#include
#include  //数学库

using namespace std;

int main() {
	while (true) {
		double a;  //定义一个双精度浮点数
		cout << "1：算圆周长 2：算圆面积 3：算圆半径 4：算圆直径\n";
		cin >> a;
		if (a == 1) {
			cout << "1:已知半径 2:已知直径：\n";
			cin >> a;
			if (a == 2) {
				cout << "请输入圆的直径" << "\n";
				cin >> a;
				cout << "圆的周长是：" << a * 3.14 << "\n";  //圆的周长公式：C=Πd
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
			else if (a == 1) {
				cout << "请输入圆的半径" << "\n";
				cin >> a;
				cout << "圆的周长是：" << 2 * a * 3.14 << "\n";  //圆的周长公式：C=2Πr
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
			else {
				cout << "error" << "\n";  //报错
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
		}
		else if (a == 2) {
			cout << "1:已知半径 2:已知直径：\n";
			cin >> a;
			if (a == 2) {
				cout << "请输入圆的直径" << "\n";
				cin >> a;
				a = a / 2;
				cout << "圆的面积是：" << a * a * 3.14 << "\n";  //圆的面积公式：S=(d/2)x(d/2)xΠ
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
			else if (a == 1) {
				cout << "请输入圆的半径" << "\n";
				cin >> a;
				cout << "圆的面积是：" << a * a * 3.14 << "\n";//圆的面积公式：S=Π * r * r
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
			else {
				cout << "error" << "\n"; //报错
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
		}
		else if (a == 3) {
			cout << "1:已知周长 2:已知面积：\n";
			cin >> a;
			if (a == 2) {
				cout << "请输入圆的面积" << "\n";
				cin >> a;
				a = a / 3.14;
				cout << "圆的半径是：" << sqrt(a) << "\n";  //r*r=S/Π
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
			else if (a == 1) {
				cout << "请输入圆的周长" << "\n";
				cin >> a;
				cout << "圆的半径是：" << a / 2 / 3.14 << "\n";  //r=C/2/Π
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
			else {
				cout << "error" << "\n"; //报错
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
		}
		else if (a == 4) {
			cout << "1:已知周长 2:已知面积：\n";
			cin >> a;
			if (a == 2) {
				cout << "请输入圆的面积" << "\n";
				cin >> a;
				a = a / 3.14;
				a = sqrt(a);
				cout << "圆的直径是：" << a * 2 << "\n"; //(d/2)*(d/2)=S/Π
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
			else if (a == 1) {
				cout << "请输入圆的周长" << "\n";
				cin >> a;
				cout << "圆的直径是：" << a / 3.14 << "\n"; //d=C/Π
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
			else {
				cout << "error" << "\n"; //报错
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
				cout << "\n";
			}
		}
		else {
			cout << "error" << "\n";  //报错
			cout << "\n";
			cout << "\n";
			cout << "\n";
			cout << "\n";
			cout << "\n";
		}
	}
}

编译后即可运行（我用的是Visual Studio 2022）