Format a number with commas, but keep decimals

Question

I'd like to group the digits in a double by thousands, but also output however number of decimals are actually in the number. I cannot figure out the format string.

 1000 => 1,000
 100000 => 100,000
 123.456 => 123.456
 100000.21 => 100,000.21
 100200.123456 => 100,200.123456

Disclaimers (it's not as straightforward as you think):

• Please do not point me to this question it does not answer my question
• Please do not point me to MSDN, the articles have not helped me. (If you believe I'm reading them incorrectly, read them yourself and post the correct answer)
• .toString("n") does not work, it rounds the digits

Answer 1

Try this one:

VB:

Dim vals() As Double = {1000, 100000, 123.456, 100000.21, 100200.123456}
For Each val As Double in vals
   Console.WriteLine(val.ToString("###,###.#########"))
Next val

C#:

double[] vals = new double[] {1000, 100000, 123.456, 100000.21, 100200.123456};
foreach (double val in vals)
{
    Console.WriteLine(val.ToString("###,###.#########"));
}

The problem is that there is no format to handle an arbitrary number of decimals. However, since you can only store a very limited precision, you can just use that and add a few more # characters as needed to cover it, assuming you're willing to let it cut off any insignificant 0's.

And the MSDN link you posted is the exact place you'd go to read how to do this.

Answer 2

This appears to do exactly what you want:

public void Code(params string[] args)
{
 Print(1000);
 Print(100000);
 Print(123.456);
 Print(100000.21 );
 Print(100200.123456);
}

void Print(double n)
{
 Console.WriteLine("{0:###,###.#######}", n);
}

1,000
100,000
123.456
100,000.21
100,200.123456

Answer 3

Try simply use "#,#", this adds the commas for thousands et al, but I don't know if it will keep the decimals, otherwise "#,###.####################", or any number of '#' symbols that you want after the decimal.

Answer 4

You can create a custom format string .ToString("###,###.######") Custom Numeric Format Strings

Answer 5

This could be a little slow, but it will do what you want.

public static string FormatNumber(double num)
{
    string s = num.ToString();
    string result = "";

    if(s.IndexOf('.') != -1)
    {
     result = s.Substring(s.IndexOf('.'));
     s = s.Substring(0, s.IndexOf('.'));
    }

    while (s.Length > 3)
    {
     result = "," + s.Substring(s.Length - 3);
     s = s.Substring(0, s.Length - 3);
    }
    if (s.Length == 0)
     return result.Substring(1);
    return s + result;
}