c# 字符串处理

private void button1_Click(object sender, EventArgs e)   
 {   
     this.textBox1.Text = "10005";   
 }   
//给字符串加.   
 private void Form1_Load(object sender, EventArgs e)   
 {   
     this.textBox1.Text = "10005";   
     string a = textBox1.Text;   
     string var1 = "";             
     for (int i = 0; i < a.Length; i++)   
     {                               
        var1 += String.Format(a[i] + "{0}", i < a.Length - 1 ? "." : "");     
     }   
     this.textBox1.Text = var1;   
 } 
  
输出格式1.0.0.0.5