creating a web calculator
<p>I created a web application on c#, the application is calculator that will display the result on text box. I am having error on the tag, which I used for storing the numbers. The error is <strong>"Tag not recognized"</strong>. how to fix it.</p>

<pre><code>protected void BtnPlusMinus_Click(object sender, EventArgs e)
{
    if (txtNumber1.Text.Contains("-"))
    {
        txtNumber1.Text = txtNumber1.Text.Remove(0, 1);
    }
    else
    {
        txtNumber1.Text = "-" + txtNumber1.Text;
    }

}

protected void BttDecimal_Click(object sender, EventArgs e)
{
    CheckifEqual();
    if (txtNumber1.Text.Contains("."))
    {
        return;
    }
    else
    {
        txtNumber1.Text = txtNumber1.Text + ".";
    }
}

protected void Btt10_Click(object sender, EventArgs e)
{
    if (txtNumber1.Text == "")
    {
       return;
    }

    else
    {
        Plus = true;

        txtNumber1.Tag = txtNumber1.Text;
        txtNumber1.Text = "";
    }
}

protected void ButtEquls_Click(object sender, EventArgs e)
{
    if (Plus)
    {

        Decimal dec = Convert.ToDecimal(txtNumber1.Text) + Convert.ToDecimal(txtNumber1.Text);
        txtNumber1.Text = dec.ToString();

    }
    if (multiply)
    {
        Decimal dec = Convert.ToDecimal(txtNumber1.Text) * Convert.ToDecimal(txtNumber1.Text);
        txtNumber1.Text = dec.ToString();


    }
    if (Minus)
    {
        Decimal dec = Convert.ToDecimal(txtNumber1.Text) - Convert.ToDecimal(txtNumber1.Text);
        txtNumber1.Text = dec.ToString();
    }
    if (divide)
    {

        Decimal dec = Convert.ToDecimal(txtNumber1.Text) / Convert.ToDecimal(txtNumber1.Text);
        txtNumber1.Text = dec.ToString();
    }


}
protected void Btt1_Click(object sender, EventArgs e)
{
    CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + "1";
}
private void CheckifEqual()
{
    if (equal)
    {
        txtNumber1.Text = "";
        equal = false;
    }

    //txtNumber1.Text = txtNumber1.Text + " 1";
}
protected void Btt2_Click(object sender, EventArgs e)
{
    CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + " 2";


}

protected void Btt13_Click(object sender, EventArgs e)
{
    CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + " 3";
}
protected void Btt04_Click(object sender, EventArgs e)
{

    CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + " 4";
}
protected void Btt5_Click(object sender, EventArgs e)
{

    CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + " 5";
}
protected void Btt06_Click(object sender, EventArgs e)
{

    CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + " 6";
}
protected void Btt07_Click(object sender, EventArgs e)
{

    CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + " 7";
}
protected void Btt08_Click(object sender, EventArgs e)
{

    CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + " 8";
}
protected void Btt09_Click(object sender, EventArgs e)
{

    CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + " 9";
}
protected void Btt0_Click(object sender, EventArgs e)
{

    //CheckifEqual();
    txtNumber1.Text = txtNumber1.Text + " 0";
}

protected void ButClear_Click(object sender, EventArgs e)
{
    Plus = Minus = multiply = divide = false;
    txtNumber1.Text = "";
    txtNumber1.Tag = "";
}
protected void BttPlusMinus_Click(object sender, EventArgs e)
{
    if (txtNumber1.Text.Contains("-"))
    {
        txtNumber1.Text = txtNumber1.Text.Remove(0, 1);
    }
    else
    {
        txtNumber1.Text = "-" + txtNumber1.Text;
    }

}
protected void Btt9_Click(object sender, EventArgs e)
{
    if (txtNumber1.Text == "")
    {

        return;

    }

    else
    {

        Minus = true;

        txtNumber1.Tag = txtNumber1.Text;
        txtNumber1.Text = "";

    }
}
protected void BttDivide_Click(object sender, EventArgs e)
{
    if (txtNumber1.Text == "")
    {
        return;
    }

    else
    {
        divide = true;

        txtNumber1.Tag = txtNumber1.Text;
        txtNumber1.Text = "";
    }
}

protected void Multiply_Click(object sender, EventArgs e)
{
    if (txtNumber1.Text == "")
    {
        return;
    }

    else
    {
        multiply = true;

        txtNumber1.Tag = txtNumber1.Text;
        txtNumber1.Text = "";
    }
}
</code></pre>

<p>}</p>
