private void ComboBox1_SelectedIndexChanged(System.Object sender, 
    System.EventArgs e)
{

    // Cast the sender object back to a ComboBox.
    ComboBox ComboBox1 = (ComboBox) sender;

    // Retrieve the selected item.
    string selectedString = (string) ComboBox1.SelectedItem;

    // Convert it to lowercase.
    selectedString = selectedString.ToLower();

    // Declare the current size.
    float currentSize;

    // Switch on the selected item. 
    switch(selectedString)
    {

            // If Bigger is selected, get the current size from the 
            // Size property and increase it. Reset the font to the
            //  new size, using the current unit.
        case "bigger":
            currentSize = Label1.Font.Size;
            currentSize += 2.0F;
            Label1.Font = new Font(Label1.Font.Name, currentSize, 
                Label1.Font.Style, Label1.Font.Unit);

            // If Smaller is selected, get the current size, in points,
            // and decrease it by 1.  Reset the font with the new size
            // in points.
            break;
        case "smaller":
            currentSize = Label1.Font.SizeInPoints;
            currentSize -= 1;
            Label1.Font = new Font(Label1.Font.Name, currentSize, 
                Label1.Font.Style);
            break;
    }
}

//引入命名空间
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

public class FormPaintEvent : System.Windows.Forms.Form
{
  private System.ComponentModel.Container components = null;

  public FormPaintEvent()
  {
    InitializeComponent();
    this.Paint += new System.Windows.Forms.PaintEventHandler(this.Form1_Paint);
  }

  protected override void Dispose( bool disposing )
  {
    if( disposing )
    {
      if (components != null) 
      {
        components.Dispose();
      }
    }
    base.Dispose( disposing );
  }

  private void InitializeComponent()
  {
    this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
    this.ClientSize = new System.Drawing.Size(292, 273);
    this.Text = "Form1";
  }
  [STAThread]
  static void Main() 
  {
    Application.Run(new FormPaintEvent());
  }

  private void Form1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
  {
    Graphics g = e.Graphics;
    g.DrawString("String...", new Font("Times New Roman", 20), new SolidBrush(Color.Black), 40, 10);
  }
}

//引入命名空间
using System;
using System.Drawing;
using System.Windows.Forms;
   
class HowdyWorld: Form
{
     public static void Main()
     {
          Application.Run(new HowdyWorld());
     }
     public HowdyWorld()
     {
          ResizeRedraw = true; 
          MinimumSize = SystemInformation.MinimumWindowSize + new Size(0,1);
          
     }
     protected override void OnPaint(PaintEventArgs pea)
     {
          DoPage(pea.Graphics, ForeColor,ClientSize.Width, ClientSize.Height);
     }     
     protected void DoPage(Graphics grfx, Color clr, int cx, int cy)
     {
          Font  font   = new Font("Times New Roman", 10, FontStyle.Italic);
          SizeF sizef  = grfx.MeasureString(Text, font);
          float fScale = Math.Min(cx / sizef.Width, cy / sizef.Height);
   
          grfx.DrawString(Text, font, new SolidBrush(clr), 
                          (cx  - sizef.Width ) / 2, (cy - sizef.Height) / 2);
     }
}