Add a number in textbox

using System;
public class Program
{
    public static void Main()
    {
        int x = 1;
        string s = x.ToString("000");
        Console.WriteLine(s);
        x = 1+9;
        s = x.ToString("000");
        Console.WriteLine(s);
        x = 1+99;
        s = x.ToString("000");
        Console.WriteLine(s);
    }
}

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        TextBox1.Text = "001";
    }
}
protected void btnAdd_Click(object sender, EventArgs e)
{
    string print = "";
    string str1 = TextBox1.Text;
    Int32 minLen = 3;
    Int32 intVal = Convert.ToInt32(str1);
    Int32 valLen = intVal.ToString().Length;

    int i = (intVal + 1).ToString().Length;
    while(i < minLen)
    {
        print = print + "0";
        i++;
    }
    print = print + (intVal + 1).ToString();
    TextBox1.Text = print;
}

string str1 = TextBox1.Text;
Int32 intVal = Convert.ToInt32(str1);
TextBox1.Text = (intVal + 1).ToString("00#");

private string intToPaddedZeroString(int i, int nZeroes)
{
    return i.ToString(zeroes.Substring(0, nZeroes));
}

// test in some method or EventHandler

for (int i = 1; i < 101; i++)
{
   SomeTextBox.AppendText(intToPaddedZeroString(i, 3) + Environment.NewLine);
}