根据字符对字符串进行分行

 1         private void button1_Click(object sender, EventArgs e)
 2         {
 3             if (textBox1.Text != string.Empty&&textBox3.Text!=string.Empty)
 4             {   if(button1.Text.Equals("清空"))
 5                     {   //清空内容
 6                      textBox1.Text = "";
 7                      textBox2.Text = "";
 8                      textBox3.Text = "";
 9                      button1.Text = "开始";
10                     }
11                 StringBuilder P_stringbuilder =//创建字符串处理对象
12                     new StringBuilder(textBox1.Text);
13                 for (int i = 0; i <P_stringbuilder.Length; i++)
14                 {//循环
15                     if (P_stringbuilder [i] ==textBox3.Text[0])
16                     {//判断是否符合
17                         P_stringbuilder.
18                         Insert(++i, Environment.NewLine);//换行输出
19                             textBox2.Text =P_stringbuilder.ToString ();
20                         button1.Text = "清空";
21                     }
22                 }
23             }
24             else { MessageBox.Show("你还没有输入┗|｀O′|┛ 嗷~~","提示："); }
25         }