模拟画图功能

模拟计算机的画图功能，能够模拟画圆和长方形的功能。程序主要功能如下：
① 提供一个如下的主菜单。

*******************************
1. Circle (圆)
2. Rectangle (长方形)
0. Exit (退出)
*******************************

② 不断接受用户的选择（整数），直至用户选择 0 为止。如果用户输入了系统尚未支持的选择（比如 3），则给出相应的提示信息，并继续选择。
③ 如果用户选择了圆或长方形，则进一步提示用户输入两个点，分别称为起点和终点，如下图所示。坐标仅考虑正整数的情况。要求终点的坐标大于起点的坐标，否则给出相关的提示信息并返回主菜单。
④ 模拟画出圆和长方形。画圆时，要计算 startPoint 和 endPoint 所构成的正方形的内切圆的圆心和半径。若 startPoint 和 endPoint 所构成的不是正方形，则给出相关的提示信息并返回主菜单。

#include <iostream>
#include <iomanip>
#include <string>
using namespace std;

// 表示平面上点的结构体
struct Point {
	double x;
	double y;
};

// 显示主菜单
void displayMenu();

// 得到用户输入的两个点
void getTwoPoints(struct Point* p1, struct Point* p2);

// 以 (x, y) 的形式打印点
void printPoint(struct Point* p);

// 画圆的函数
void drawCircle(struct Point* p1, struct Point* p2);

// 画长方形的函数
void drawRectangle(struct Point* p1, struct Point* p2);

int main() {
	int choice = 1;
	struct Point startP, endP;

	while (choice) {
		displayMenu();
		cin >> choice;

		switch (choice) {
		case 1:
			getTwoPoints(&startP, &endP);
			drawCircle(&startP, &endP);
			break;
		case 2:
			getTwoPoints(&startP, &endP);
			drawRectangle(&startP, &endP);
			break;
		case 0:
			cout << "Good bye!\n";
			break;
		default:
			cout << "Not supported! Please select again!\n";
			break;
		}
	}
	return 0;
}

void displayMenu() {
	cout << "*********************************" << endl;
	cout << "  1. Circle（圆）                 " << endl;
	cout << "  2. Rectangle（长方形）          " << endl;
	cout << "  0. Exit（退出）                 " << endl;
	cout << "*********************************" << endl;
	cout << "Please select the shape: " << endl;
}

void getTwoPoints(struct Point* p1, struct Point* p2) {
	double x1, y1, x2, y2;
	while (true) {
		cout << "The end point should be greater than the start point. " << endl;
		cout << "Please input the coordinate (x, y) of the start point: ";
		cin >> x1 >> y1;
		cout << "Please input the coordinate (x, y) of the end point: ";
		cin >> x2 >> y2;
		if (x2 > x1 && y2 > y1) {
			p1->x = x1;
			p1->y = y1;
			p2->x = x2;
			p2->y = y2;
			break;
		} else {
			cout << "Not supported! Please input again!" << endl;
		}
	}
}

void printPoint(struct Point* p) {
	cout << "(" << setprecision(6) << p->x << ", "
		<< setprecision(6) << p->y << ")";
}

void drawCircle(struct Point* p1, struct Point* p2) {
	double xDiffer = p2->x - p1->x;
	double yDiffer = p2->y - p1->y;
	if (xDiffer == yDiffer) {
		double radius = xDiffer / 2;
		double xCenter = p1->x + radius;
		double yCenter = p1->y + radius;
		cout << "Draw a circle at center (" << setprecision(6) << xCenter << ", "
			<< setprecision(6) << yCenter << ") with radius "
			<< setprecision(6) << radius << endl;
	} else {
		cout << "Not a circle! Please select again!\n";
	}
}

void drawRectangle(struct Point* p1, struct Point* p2) {
	double xDiffer = p2->x - p1->x;
	double yDiffer = p2->y - p1->y;
	cout << "Draw a rectangle at topleft ";
	printPoint(p1);
	cout<<", whose width is " << setprecision(6)<< xDiffer 
		<< " and height is " << setprecision(6) << yDiffer << endl;
}