Question

How to validate a TextBox field against a Natural Number? User are restricted to input natural number (e.g. 1,2,3..99999) and if not, a MessageBox is shown.

Currently I’m using the following code (assuming the natural number does not go beyond two digits):

Regex isPositiveNum2 = new Regex("[1-9]");
Regex isPositiveNum = new Regex("[1-9][1-9]");
if (isPositiveNum.IsMatch(textbox1.Text) == true || 
    isPositiveNum2.IsMatch(textbox1.Text) == true)
{
    /* Do something */
}
else
{
    MessageBox.Show("Hey! This is not a Natural Number");
    textbox1.Text = "1";
}

This works alright, but I’m sure it’s not the best approach. Hope something can suggest something better.

Answer 1

Use the built in parsing:

int.Parse(textbox1.Text) > 0

This will throw an exception if textbox1.Text can’t be parsed, so you may want to use TryParse instead:

int test;
if(int.TryParse(textbox1.Text, out test))
{
  // parse succeeded can check if natural
  if(test > 0)
  {
    // do something
  }
}