如果我没有记错，那么您想添加您的文本框值将变为其他文本框.如果是这样，那么您就可以:-
在button_Click上编写以下代码:

If i am not wrong then you want to add your textbox value to some ohter textboxes. If It is so then here you go:-
On button_Click write following code:

protected void button_Click(object sender, EventArgs e)
{
   //first retrieve the value of your textbox and store it into string
   string firstvalue = textBox1.Text;
   //then assign this string value to your rest of the textbox or label.
   textBox2.Text = firstvalue;
   textBox3.Text = firstvalue;
   label1.Text = firstvalue;
 }

希望对您有帮助.

祝你好运.

I hope it will help you.

Good luck.

尝试使用此代码

try using this code

protected void button_Click(object sender, EventArgs e)
 {
    
   string multivalue = textBox1.Text.ToString();
  
    textBox2.Text = multivalue;
    textBox3.Text = multivalue;
   
  }