C# How to format a double to one decimal place without rounding

Question

I need to format a double value to one decimal place without it rounding.

double value = 3.984568438706
string result = \"\";

What I have tried

Answer 1

ToString() doesn't do it. You have to add extra code. The other answers show math approaches, my approach below is kind of outside-the-box.

string result = value.ToString();
Console.WriteLine("{0}", result.Substring(0, result.LastIndexOf('.') + 2));

This is a fairly simple brute force approach, but it does the trick when the decimal is a '.'. Here's an extension method to ease the pain (and deals with the decimal point).

public static class Extensions
{
    public static string ToStringNoTruncate(this double me, int decimalplaces = 1)
    {
        string result = me.ToString();
        char dec = System.Globalization.CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator[0];
        return result.Substring(0, result.LastIndexOf(dec) + decimalplaces + 1);
    }
}