how not to allow decimal or float numbers in c sharp?

Solution 1 may fail on possible cultural differences.
Try:

int price = int.Parse(priceTextBox.Text, CultureInfo.CurrentCulture);

You get the numeric value from this.
Throws a FormatException if the .Text is not an integer value.
Use whatever is appropriate instead of CultureInfo.CurrentCulture for different cultures,
e.g. CultureInfo.InvariantCulture

If you'd rather some different error handling for the parse failures:

int price;
if (!int.TryParse(priceTextBox.Text, NumberStyles.Integer, CultureInfo.CurrentCulture, out price))
{
  // Whatever handling for not a simple integer goes here.
}
// price has the value here