Double to string with mandatory decimal point

Question

This is probably dumb but it's giving me a hard time. I need to convert/format a double to string with a mandatory decimal point.

1         => 1.0
0.2423423 => 0.2423423
0.1       => 0.1
1234      => 1234.0

Basically, I want to output all decimals but also make sure the rounded values have the redundant .0 too. I am sure there is a simple way to achieve this.

Answer 1

Use double.ToString("N1"):

double d1 = 1d;
double d2 = 0.2423423d;
double d3 = 0.1d;
double d4 = 1234d;
Console.WriteLine(d1.ToString("N1"));
Console.WriteLine(d2.ToString("N1"));
Console.WriteLine(d3.ToString("N1"));
Console.WriteLine(d4.ToString("N1"));

Demo

Standard Numeric Format Strings

The Numeric ("N") Format Specifier

Update

(1.234).ToString("N1") produces 1.2 and in addition to removing additional decimal digits, it also adds a thousands separator

Well, perhaps you need to implement a custom NumberFormatInfo object which you can derive from the current CultureInfo and use in double.ToString:

var culture = CultureInfo.CurrentCulture;
var customNfi = (NumberFormatInfo)culture.NumberFormat.Clone();
customNfi.NumberDecimalDigits = 1;
customNfi.NumberGroupSeparator = "";
Console.WriteLine(d1.ToString(customNfi));

Note that you need to clone it since it's readonly by default.

Demo

Answer 2

There is not a built in method to append a mandatory .0 to the end of whole numbers with the .ToString() method, as the existing formats will truncate or round based on the number of decimal places you specify.

My suggestion is to just roll your own implementation with an extension method

public static String ToDecmialString(this double source)
{
    if ((source % 1) == 0)
        return source.ToString("f1");
    else
        return source.ToString();

}

And the usage:

double d1 = 1;
double d2 = 0.2423423;
double d3 = 0.1;
double d4 = 1234;
Console.WriteLine(d1.ToDecimalString());
Console.WriteLine(d2.ToDecimalString());
Console.WriteLine(d3.ToDecimalString());
Console.WriteLine(d4.ToDecimalString());

Results in this output:

1.0
0.2423423
0.1
1234.0