Textbox should accept numbers from 0 to 366

at the keypress event of textbox write

if (!(e.KeyChar >= '0' && e.KeyChar <= '9'))
                e.Handled = true;

it will secure to enter only numbers.
and as i getting your second question is about limitation of numbers enetered in Textbox. for this you can use MaxLength property of textnox

How about you use NumericUpdown Control[http://msdn.microsoft.com/en-us/library/729xt55s.aspx[^]]? It does what you want. It has Minimum, Maximum, Skip properties, and takes in a number.

Just put a condition on the content.

bool contLetter = false;
string reqNumber = textBox1.Text.Trim();
for (int i = 0; i < reqNumber.Length; i++)

{
if (!char.IsNumber(reqNumber[i]))
{
contLetter = true;
}
}
if (contLetter)
{
// Some error label and redo enter textbox value
}

Then once you have confirmed a number, confirm it's value is between the chosen ranges.

(I leave that as an excercise for the OP)

Take a look at this

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (char.IsDigit(e.KeyChar) == true)
    {
        e.Handled = false;
        if (textBox1.Text.Length > 0)
        {
            if (Convert.ToInt32(textBox1.Text) >= 36)
            {
                if (Convert.ToInt32(textBox1.Text) >= 37)
                {
                    textBox1.MaxLength = 2;
                }
                else
                {
                    textBox1.MaxLength = 3;
                }
                if (Convert.ToInt32(e.KeyChar.ToString()) > 6)
                {
                    e.Handled = true;
                    return;
                }
                else
                {
                    e.Handled = false;
                }
            }
            else
            {
                e.Handled = false;
                textBox1.MaxLength = 3;
            }
        }
        else
        {
            e.Handled = false;
        }
    }
    if (e.KeyChar == (char)Keys.Back || char.IsDigit(e.KeyChar) == true)
    {
        e.Handled = false;
    }
    else
    {
        e.Handled = true;
    }
}

Vote if is Useful.

try..

function funNumber(a) {
    if (a.value > 366) {
        a.value = a.value.substring(0, 3);
        return true;
    }
    else {
        if (event.keyCode >= 48 && event.keyCode <= 57) {
            return true;
        }
        else if (event.keyCode >= 45 && event.keyCode <= 46) {
        }
        else {
            event.returnValue = false;
            return false;
        }
    }
}

on page load

protected void Page_Load(object sender, EventArgs e)
   {
       txtUserName.Attributes.Add("onkeyup", "funNumber(this)"); 
}