Question

Well the question title may not be self explanatory, so let me go ahead and elaborate.

Consider, a TextBox that accepts only numeric value or is left empty. The value(text) entered is stored in an integer(int32) variable. The problem arises when the user enters the digit 0 or leaves the TextBox empty, as the conversion from string to int, converts an empty string to “0” as well.

So my question stands: How do I differentiate the 2 scenarios?

EDIT I figured a lot of questions may be answered by the code and exact problem(as I see it)

    if (txtOtherId.Text == string.Empty)
    {
        otherId = Convert.ToInt32(null);
    }
    else
    {
        otherId = Convert.ToInt32(txtOtherId.Text);
    }

Answer 1

What have you tried? Can we see your code?

Now, I tried the following:

int i;
i = Convert.ToInt32("");  // throws, doesn't give zero
i = int.Parse("");         // throws, doesn't give zero
bool couldParse = int.TryParse("", out i);   // makes i=0 but signals that the parse failed

So I can’t reproduce. However, if I use null instead of "", the Convert.ToInt32 does convert into zero (0). However, Parse and TryParse still fail with null.

UPDATE:

Now that I see your code. Consider changing the type of otherId from int to int? where the question mark makes it a nullable type. Then:

if (txtOtherId.Text == "")
{
    otherId = null;  // that's null of type int?
}
else
{
    otherId = Convert.ToInt32(txtOtherId.Text);   // will throw if Text is (empty again or) invalid
}

If you want to be sure no exceptions can happen, do this:

int tmp; // temporary variable
if (int.TryParse(txtOtherId.Text, out tmp))
    otherId = tmp;
else
    otherId = null;   // that's null of type int?; happens for all invalid input