刚学编程，写了个判断独立点与多边形位置关系的算法（C#）

#region Using directives

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Windows.Forms;

#endregion

namespace p_polygon
{
    partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        public int count = 0;//顶点计数

        public bool reset=false;//设复位功能标志

        private struct point//顶点结构
        {
            public float x, y;
        }

        point[] pt = new point[100];

        private float Max(float x,float y)
        {
            return(x>y?x:y);
        }

        private float Min(float x, float y)
        {
            return (x < y ? x : y);
        }

        private void Judge(point[] pt)//判断函数
        {
            float Px = float.Parse(textBox1.Text);
            float Py = float.Parse(textBox2.Text);
            float[] line = new float[99];
            float linelast;
            float flag = 1;//判断在直线左右的标志数（大于0在右，小于0在左）
            bool online = false;
            for (int i = 1; i < count; i++)
            {
                line[i - 1] = (pt[i].y - pt[i - 1].y) * Px + (pt[i - 1].x - pt[i].x) * Py +
                    (pt[i].x - pt[i - 1].x) * pt[i - 1].y - (pt[i].y - pt[i - 1].y) * pt[i - 1].x;
                if (line[i - 1] == 0 && Px <= Max(pt[i].x, pt[i - 1].x) && Px >= Min(pt[i].x, pt[i - 1].x))
                    online = true;
                flag *= line[i - 1];
                if (i == count - 1)
                {
                    linelast = (pt[0].y - pt[i].y) * Px + (pt[i].x - pt[0].x) * Py +
                    (pt[0].x - pt[i].x) * pt[i].y - (pt[0].y - pt[i].y) * pt[i].x;
                    flag *= linelast;
                    if (flag == 0)
                    {
                        if (Px <= Max(pt[i].x, pt[0].x) && Py >= Min(pt[i].x, pt[0].x))
                            online = true;
                        else
                            online = false;
                    }
                }

                if ((flag < 0 && online == false) || (flag == 0 && online == false))
                {
                    MessageBox.Show("the isolated point is outside the polygon");
                    break;
                }
                else if (flag == 0 && i == count - 1 && online == true)
                {
                    MessageBox.Show("the isolated point is on the border of the polygon");
                    break;
                }
                else if (flag > 0 && i == count - 1)
                {
                    MessageBox.Show("the isolated point is inside the polygon");
                    break;
                }

            }

        }

        //复位函数
        private void Resetall()
        {
            textBox1.Text = "";
            textBox2.Text = "";
            textBox3.Text = "";
            textBox4.Text = "";
            count = 0;
            label1.Text = "0";
            reset = true;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (textBox3.Text != "" && textBox4.Text != "")
            {

                if (count < 100)
                {
                    pt[count].x = float.Parse(textBox3.Text);
                    pt[count].y = float.Parse(textBox4.Text);
                    count++;
                    label1.Text = count.ToString();
                    reset = false;
                }
                else
                    MessageBox.Show("Only 100 vertexes support!");
            }
            else
                MessageBox.Show("Please input necessary data!");
        }

        private void button2_Click(object sender, EventArgs e)
        {
            if (reset == false)
            {
                if (textBox1.Text != "" && textBox2.Text != "" && textBox3.Text != "" && textBox4.Text != "")
                    Judge(pt);
                else
                    MessageBox.Show("Please input necessary data!");
            }
            else
                MessageBox.Show("All data Cleared! Input again.");

        }

        private void button3_Click(object sender, EventArgs e)
        {
            Resetall();
        }

        private void button4_Click(object sender, EventArgs e)
        {
            MessageBox.Show("When you input the coordinates of vertexes,\nyou must ensure that the vertexes are ORDINAL\nand the polygon is at the RIGHT side of the line\nfrom PREVIOUS vertex to CURRENT vertex.\nOr else, there must be ERROR!\n\nPLEASE REMEMBER! Good Luck!\n\n\npoint & polygon v1.0 <<ICEBOY 2005.1.2>>",
                "Attention!",MessageBoxButtons.OK,MessageBoxIcon.Information);
        }
    }
}

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