Why doesn't the code in C# work?

Question

C++ / C#

Hello.
There is a code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {

        Bitmap gBitmap;
        Pen MyPen0;
        Pen MyPen;
        Graphics gScreen;
        Bitmap bitmap;
        TElement[] Element;

        public Form1()
        {
            InitializeComponent();

        }

        public struct TElement
        {
            public int x;
            public int y;
            public int inf;
            public Color color;
        }

        void Sort()
        {
            int L = Element.Length;
            for (int i = 1; i <= L - 1; i++)
                for (int j = i; j <= L - 1; j++)
                {
                    TElement tmp;
                    if (Element[j - 1].inf > Element[j].inf)
                    {
                        tmp = Element[j];
                        Element[j] = Element[j - 1];
                        Element[j - 1] = tmp;
                    }
                }
        }

        void SetRandom()
        {
            int L = Element.Length;
            Random rnd = new Random();
            for (int i = 0; i <= L - 1; i++)
            {
                Element[i].x = 100;
                Element[i].y = 20 + i * 40;
                Element[i].color = Color.Black;
                Element[i].inf = rnd.Next(100);
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            SetRandom();
            Drawing(-1, -1);
        }

        void Drawing(int n, int m)
        {
            const int d = 15;
            int L = Element.Length;
            string s;
            SizeF size;
            gBitmap.Clear(Color.White);
            for (int i = 0; i <= L - 1; i++)
            {
                MyPen.Color = Element[i].color;
                gBitmap.DrawEllipse(MyPen, Element[i].x - d, Element[i].y - d, 2 * d, 2 * d);
                s = Convert.ToString(Element[i].inf);
                size = gBitmap.MeasureString(s, Font);
                gBitmap.DrawString(s, Font, Brushes.Black,  Element[i].x - size.Width / 2,
                Element[i].y - size.Height / 2);
            }
            if (n != -1)
            {
                MyPen0.Color = Color.Black;
                gBitmap.DrawLine(MyPen0, 120, Element[n].y, 140, Element[n].y);
                s = "I = " + Convert.ToString(n);
                size = gBitmap.MeasureString(s, Font);
                gBitmap.DrawString(s, Font, Brushes.Black, 150, Element[n].y - size.Height / 2);
            }
            if (m != -1)
            {
                MyPen0.Color = Color.Red;
                gBitmap.DrawLine(MyPen0, 120, Element[m].y, 140,
                Element[m].y);
                s = "J = " + Convert.ToString(m);
                size = gBitmap.MeasureString(s, Font);
                gBitmap.DrawString(s, Font, Brushes.Black, 150, Element[m].y - size.Height / 2);
            }
            gScreen.DrawImage(bitmap, ClientRectangle);
        }


        void Change(int n1, int n2, int n, int m)
        {
            Element[n1].color = Color.Red;
            Element[n2].color = Color.Red;
            int x1 = Element[n1].x;
            int y1 = Element[n1].y;
            int x2 = Element[n2].x;
            int y2 = Element[n2].y;
            double x;
            for (int t = 1; t <= 15; t++)
            {
                x = (y2 - y1) * t / 15;
                Element[n1].y = y1 + (int)(x);
                switch (t)
                {
                    case 1:
                    case 2:
                    case 3:
                    case 4:
                        x = 40 * t / 4;
                        Element[n2].x = x1 - (int)(x);
                        break;
                    case 5:
                    case 6:
                    case 7:
                    case 8:
                    case 9:
                    case 10:
                    case 11:
                        x = (y1 - y2) * (t - 4) / 7;
                        Element[n2].y = y2 + (int)(x);
                        break;
                    case 12:
                    case 13:
                    case 14:
                    case 15:
                        x = 40 * (t - 11) / 4;
                        Element[n2].x = x1 - 40 + x;
                        break;
                }
                Drawing(n, m);
                Thread.Sleep(100);
            }
            Element[n1].color = Color.Black;
            Element[n2].color = Color.Black;
            Drawing(n, m);
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            gScreen = CreateGraphics();
        }
    }
}

The compiler complains about:
gBitmap.Clear(Color.White); - does not see the clear method, does not see the DrawEllipse, MeasureString method. Because of which ??? Thanks

Answer 1

Well, because the bitmap does not have such methods. These are the methods of Graphics. Use

Graphics g = Graphics.FromImage(gBitmap);
g.Clear(Color.White);

etc.

Answer 2

Why should you see? Are you from Delphi?

var g = Graphics.FromImage(gBitmap);
g.DrawEllipse(...)
g.MeasureString(...)

public struct TElement
it is not customary to write type names with the letter T here