Just learned to program, wrote an algorithm to determine the relationship between independent point and polygon position (C #)

Programming | algorithm #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;//Vertex count

public bool reset=false;//set reset function mark

Private struct point//vertex structure
{
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)//Judgment function
{
float Px = float. Parse (TextBox1.Text);
float Py = float. Parse (TextBox2.Text);
Float[] line = new float[99];
float Linelast;
Float flag = 1;//To determine the number of flags in line or so (greater than 0 on the right, less than 0 in the left)
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
}

}


}

Reset function
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 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 this vertexes are ordinal\nand the Polyg ' On ' right side of the ' Line\nfrom PREVIOUS vertex to current vertex.\nor else, there must as Error!\n\nplease mber! Good Luck!\n\n\npoint & Polygon v1.0 <<iceboy 2005.1.2>> ",
"attention!", messageboxbuttons.ok,messageboxicon.information);
}
}
}