CODEWITHSUNDEEP
c#exceptionthrow
Patrick Daniels
Patrick Daniels

Reputation: 51

String not being thrown

I am fairly new to C#. Although throwing the exceptions for the other conditions work fine, the string (or lack of entry would be a better term to use) does not work. It instead goes straight to catch (FormatException) message.

I know that I could put the same statement if (txtSubtotal.Text == "") in the aforementioned catch statement, and it would work fine, but I am really curious as to why I cannot do this by throwing a new exception.

private void btnCalculate_Click(object sender, EventArgs e)
{
    try
    {
        decimal subtotal = Decimal.Parse(txtSubtotal.Text);
        {
            if (txtSubtotal.Text == "")
                throw new Exception("Subtotal is a Required Field.");

            if (subtotal <= 0)
                throw new Exception("Subtotal must be greater than 0");

            if (subtotal >= 10000)
                throw new Exception("Subtotal must be less than 10000");
        }

        decimal discountPercent = .25m;
        decimal discountAmount = subtotal * discountPercent;
        decimal invoiceTotal = subtotal - discountAmount;

        discountAmount = Math.Round(discountAmount, 2);
        invoiceTotal = Math.Round(invoiceTotal, 2);

        txtDiscountPercent.Text = discountPercent.ToString("p1");
        txtDiscountAmount.Text = discountAmount.ToString();
        txtTotal.Text = invoiceTotal.ToString();

        txtSubtotal.Focus();
    }
    catch (FormatException)
    {
        MessageBox.Show("Please enter a valid number for the Subtotal field.", "Entry Error");
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message + "\n" + "\n", "Entry Error");
    }
}

Upvotes: 0

Views: 83

Answers (3)

Russell Jonakin
Russell Jonakin

Reputation: 1996

This behavior is due to your string being null or empty and the code trying to parse a null or empty string to a Decimal.

It would be better to check the string before trying to parse it. Also you can check the contents of a string easily with the string.IsNullOrWhitespace method from the string class.

Like this:

try
{ 
    if (string.IsNullOrWhitespace(txtSubtotal.Text))
        throw new Exception("Subtotal is a Required Field.");

    decimal subtotal = Decimal.Parse(txtSubtotal.Text); 

    //rest of your code.

With the code like this and the string is null or white space, the basic Exception will be thrown...but if the string is a NOT null or white space AND it is not a valid number format either, then the code will throw the FormatException.

Upvotes: 0

Trevor Ash
Trevor Ash

Reputation: 633

Couple things here, first I think there is a logic issue confusing your expected result. Take this excerpt...

decimal subtotal = Decimal.Parse(txtSubtotal.Text);
{
    if (txtSubtotal.Text == "")
    throw new Exception("Subtotal is a Required Field.");
...

Decimal.Parse is always going to throw a FormatException on an empty string, or any other value where it can't convert to a decimal. This means the next if condition never gets executed. And if it did get executed, it'll never be true because you just proved it otherwise with a successful Decimal.Parse.

Upvotes: 0

sujith karivelil
sujith karivelil

Reputation: 29026

The method Decimal.Parse() will throws FormatExceptions if the parameter(txtSubtotal.Text) to the method is not convertible. To avoid this you can You trust Decimal.TryParse() for doing the same, without any try..catch try the following code:

decimal subtotal;
if (Decimal.TryParse(txtSubtotal.Text, out subtotal))
{
    if (subtotal <= 0)
       MessageBox.Show("Subtotal must be greater than 0");
    else if (subtotal >= 10000)
        MessageBox.Show("Subtotal must be less than 10000");
    else
    { 
     // Process your code here
    }
}
else
{
    MessageBox.Show("Invalid Input! Subtotal Expecting a Decimal value");
}

Upvotes: 2

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