Decimal rounding not always working correctly

Question

I'm using Decimals in VB.NET to hold values for currency. It is possible on my website to add a discount to an item, which is inputted into a text box and then the value is retrieved in the code-behind.

Dim discountValue As Decimal = 0
discountValue = Decimal.Round(Convert.ToDecimal(txtDiscount.Text), 2)
lblDiscount.Text = "£" & discountValue.ToString()

However, when I view the label after adding the discount, it is not rounded to 2 decimal points.

Is there any reason this is not working? What am I doing wrong in this approach?

Note: I'm using ASP.NET VB.NET and the page is wrapped inside an UpdatePanel.

Why not [letting `String.Format` round it](https://stackoverflow.com/a/7076918/107625) for you? E.g. `String.Format("{0:0.00}", discountValue);` or `discountValue.ToString("0.00")`. — Uwe Keim, Aug 22 '17 at 13:44
Have you tried putting a break point to see where the error is? I copy/pasted your code in a console application and it's working. What is the value of txtDiscount.Text ? — the_lotus, Aug 22 '17 at 13:49
@UweKeim I didn't even think of that!! It works now, thank you :) — a--, Aug 22 '17 at 13:49
@MorganLane if String.Format worked but ToString didn't, then the rounding setting is in your culture information, you should check the value of CurrentCulture.NumberFormat.NumberDecimalDigits — the_lotus, Aug 22 '17 at 13:59

score 3 · Accepted Answer · answered Aug 22 '17 at 13:49

3

It's because ToString() just formats it without the decimal points if the number is *.00
Change this line:

lblDiscount.Text = "£" & discountValue.ToString("N2")

answered Aug 22 '17 at 13:49

MatSnow

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Or `lblDiscount.Text = discountValue.ToString("C2")` to automatically use the currency symbol for the current culture. – Blackwood Aug 22 '17 at 13:57
@Blackwood Yeah, even better, depending on the needs of the OP. – MatSnow Aug 22 '17 at 14:04
I like this way more, saves me having to worry about the currency symbol in the future. – a-- Aug 22 '17 at 14:05
1

@MorganLane Now I think about it. `lblDiscount.Text = discountValue.ToString("C")` should automatically use the appropriate number of decimal places for the current culture (2 in the case of UK and US). – Blackwood Aug 22 '17 at 14:28

Decimal rounding not always working correctly

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