currently i working for a button click event where i want to adding text into textarea content

For example

textbox A = "name"
dropdownlist = "string"

after click button, it will be come

output

public class abc { 

private string name;
}

when i click on the button for second time with textbox A = "job"
then it will become

output

public class abc { 

private string name;
private string job;
}

i only can make it by displaying the same text for several times, where the output is like

output

public class abc { 

private string name;
private string name;
private string name;
}

currently this is my code behind

String temp = "";
    String classtemp = txtclassname.Text;
                String vartemp = txtvariable.Text;
                String datatemp = ddldatatype.SelectedValue;

        protected void btaddvar_Click(object sender, EventArgs e)

                {

                    int rowCount = 0;

                    rowCount = Convert.ToInt32(Session["clicks"]);

                    rowCount++;

                    Session["clicks"] = rowCount;

                    for (int i = 0; i < rowCount; i++)

                   {

                    temp += "private " + datatemp + " " + vartemp + ";\n";

                   }

                    txtclasscode2.Text = "public class " + classtemp + " {\n\n" + temp.ToString() + "\n}";
        }

i know that the mistakes i have done in my for loop statement, but i can't figure it out

how to play around with it since my knowledge about c# asp.net still very poor.

Anyone can help me or give some suggestion?

You are correct. You are simply appending the same current value repeatedly. To solve this, you are going to need to store your previous entries in ViewState, Session, or other form field such that your values aren't lost between Postbacks.
Cheers.