public enum 星期
{
  星期一 = 0,
  星期二,
  星期三,
  星期四,
  星期五,
  星期六,
  星期天
}

public MainForm()
{
 //
 // The InitializeComponent() call is required 
 //for Windows Forms designer support.
 //
 InitializeComponent();
 //
 // TODO: Add constructor code 
 // after the InitializeComponent() call.
 //
 int idx = 0;
 foreach(Control c in groupBox1.Controls)
 {
  if(c is RadioButton)
  {
   ((RadioButton)c).Text = ((星期)idx).ToString();
   ((RadioButton)c).Tag = ((星期)idx);
   idx++;
  }
 }
}

void Button1Click(object sender, EventArgs e)
{
 foreach(Control c in groupBox1.Controls)
 {
  if(c is RadioButton)
  {
   if(((RadioButton)c).Checked == true)
   {
    星期 week = (星期)(((RadioButton)c).Tag);
    MessageBox.Show(week.ToString());
   }
  }
 }
}

this.groupBox1.Controls.Add(this.radioButton1);
this.groupBox1.Controls.Add(this.radioButton2);
this.groupBox1.Controls.Add(this.radioButton3);
this.groupBox1.Controls.Add(this.radioButton4);
this.groupBox1.Controls.Add(this.radioButton5);
this.groupBox1.Controls.Add(this.radioButton6);
this.groupBox1.Controls.Add(this.radioButton7);