Develop Reference

C# - invariant culture

I'm trying to convert a double to a decimal with a dot instead of a comma. I feel like I have tried every single possible way (except a working one) so I'm out of ideas.
double amount = myUsd / price;
string amountAsString = amount.ToString();
decimal value = Decimal.Parse(amountAsString, CultureInfo.InvariantCulture);
This one gives a FormatException for example.
Thanks

As Hans Passant said, if you Parse in the same way as you Format you'll avoid a lot of issues -> Use string amountAsString = amount.ToString(CultureInfo.InvariantCulture);
EDIT
Since you're passing in an exponential notation you need to tell the Parser this. This worked with your example value:
decimal value = Decimal.Parse(amountAsString, System.Globalization.NumberStyles.Float, CultureInfo.InvariantCulture);
But I suggest NOT formatting it as a Double. First convert it to a Decimal. Then parse it as a Decimal:
double amount = myUsd / price;
Decimal decAmount = (Decimal)amount;
string amountAsString = decAmount.ToString(CultureInfo.InvariantCulture);
decimal value = Decimal.Parse(amountAsString, CultureInfo.InvariantCulture);
Then it'll never get formatted in exponential notation.
Also see this C# Fiddle snippet

c# decimal keep only 2 decimals

I have a decimal number: 12.4465463455
decimal value = 12.4465463455m;
How can I round this decimal and remove extra decimals but 2 so the decimal will be 12.45 ? Please notice I don't need a string. I know how to convert this to a string with 2 decimals and rounded. But have no idea how to manipulate the decimal variable itself.

Just use Math.Round, so:
decimal value = 12.4465463455m;
decimal value2dp = Math.Round(value, 2); //2 => 2 decimal places

Wrong parsing from string to double

double value = double.Parse("4655.927411110702", CultureInfo.InvariantCulture);
Why this parsing is getting me result: 4655.9274111107025?
Somehow it adds to my number 5 at the end. How should I convert this string to double and have a correct result?

You can't. Not all numbers can be represented exactly in double precision floating point, and the closest such double to 4655.927411110702 is 4655.927411110702450969256460666656494140625, and the default formatting you're using trims off the majority of the "joke" digits.
C# does have a decimal type. Can you not use that?
decimal value = decimal.Parse("4655.927411110702", CultureInfo.InvariantCulture);

How do I convert string to decimal?

I have this textbox that accepts numbers, commas, and periods.
Let's say this textbox contains input 14,500.00
I tried to convert this number to decimal with Convert.ToDecimal(textbox.text) but it's not working. Convert.ToDecimal() to textboxes that contain input that has the format XXXX.DD are converted to decimal but input with format X,XXX.DD or any input with a thousand separator results to error:
Input string was not in correct format
Is Convert.ToDecimal() appropriate in this case?
ADDITIONAL INFO:
Here is the form. If I click 'Add', the product of 'Price' and 'Quantity' should be displayed as 'Amount' in the datagridview.
The syntax in the 'Add' button includes:
DataRow dr;
dr = dsDetail.Tables["SalesOrderDetails"].NewRow();
dr["Amount"] = Convert.ToDecimal(txtSellingPrice.Text) * Convert.ToDecimal(txtQuantity.Text);
The Amount field in my SalesOrderDetails table has the datatype decimal(18,2)

You can force a culture and use decimal.Parse
decimal d = decimal.Parse("14,500.00", CultureInfo.InvariantCulture); // 14500
Is Convert.ToDecimal() appropriate in this case?
Yes, you could also continue to use Convert.ToDecimal if you want:
d = Convert.ToDecimal("14,500.00", CultureInfo.InvariantCulture);

I would give decimal.TryParse a go
decimal d;
if(decimal.TryParse(textbox.Text, out d))
{
//do something
}

I suspect you're using a culture that defines . as the thousands separator and , as the decimal separator. If you want to force , and . as the thousands and decimal separators, respectively then use:
decimal value = Convert.ToDecimal(textbox.text,CultureInfo.InvariantCulture);
Is Convert.ToDecimal() appropriate in this case?
It's fine - the main difference is it supports more types than decimal.Parse, which only supports strings.

I agree with #matt_lethargic, but offer a more complete solution. Tested with XUnit :)
[Theory]
[InlineData("en-US","44.00")]
[InlineData("es-PE", "44,00")]
[InlineData("es-PE", "44.00")]
[InlineData("es-PE", "0.01E-15")]
[InlineData("es-PE", "0,01E-15")]
public void ParsesDeciaml(string culture, string dec)
{
CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo(culture);
decimal d;
if (!decimal.TryParse(dec, out d)
&& !decimal.TryParse(
dec,
System.Globalization.NumberStyles.Any,
System.Globalization.CultureInfo.CurrentCulture,
out d
)
&& !decimal.TryParse(
dec,
System.Globalization.NumberStyles.Any,
System.Globalization.CultureInfo.InvariantCulture,
out d
)
) Assert.False(true, dec);
}
That way you can capture values with exponential formats.

Formatting a decimal value with ToString() to have commas as thousand separators where the amount of decimal places is unknown

I have many decimals, each rounded differently:
decimal quantity = Decimal.Round(item.Quantity.Value, 2,
MidpointRounding.AwayFromZero);
decimal difference = Decimal.Round(quantity * eva, 0,
MidpointRounding.AwayFromZero);
When binding to the UI, I convert to string like this:
string Quantity = quantity.ToString("G", CultureInfo.InvariantCulture);
string Difference = difference.ToString("G", CultureInfo.InvariantCulture);
Is there a generic way to insert commas for thousand separators while keeping the original decimal rounding the same?

Try using Format.
double d = 1.234567;
String output = d.ToString("#,##0.##");
Also,
double d = 123456789.1;
string format = d.ToString().
IndexOf(NumberFormatInfo.CurrentInfo.NumberDecimalSeparator)
>=0 ? "#,##0.00" : "#,##0";
Console.WriteLine (d.ToString(format));

For anyone wondering, I ended up using String.Format(new CultureInfo("en-US"), "{0:N}", difference) and changed the N depending on how many decimal places I needed.

You can use the "N" format specifier and supply the number of digits you want any number to retain. If you want each number to potentially have a different number of digits you wall have to determine the number to supply to the format string each time.
quantity.ToString("N(digits)");
Complete documentation is at http://msdn.microsoft.com/en-us/library/dwhawy9k.aspx#NFormatString