How do I format a Decimal to a programatically con

问题:

How can I format a number to a fixed number of decimal places (keep trailing zeroes) where the number of places is specified by a variable?

e.g.

int x = 3;
Console.WriteLine(Math.Round(1.2345M, x)); // 1.234 (good)
Console.WriteLine(Math.Round(1M, x));      // 1   (would like 1.000)
Console.WriteLine(Math.Round(1.2M, x));    // 1.2 (would like 1.200)

Note that since I want to control the number of places programatically, this string.Format won't work (surely I ought not generate the format string):

Console.WriteLine(
    string.Format("{0:0.000}", 1.2M));    // 1.200 (good)

Should I just include Microsoft.VisualBasic and use FormatNumber?

I'm hopefully missing something obvious here.

回答1:

Try

decimal x = 32.0040M;
string value = x.ToString("N" + 3 /* decimal places */); // 32.004
string value = x.ToString("N" + 2 /* decimal places */); // 32.00
// etc.

Hope this works for you. See

http://msdn.microsoft.com/en-us/library/dwhawy9k.aspx

for more information. If you find the appending a little hacky try:

public static string ToRoundedString(this decimal d, int decimalPlaces) {
    return d.ToString("N" + decimalPlaces);
}

Then you can just call

decimal x = 32.0123M;
string value = x.ToRoundedString(3);  // 32.012;

回答2:

Try this to dynamically create your own format string without having to use multiple steps.

Console.WriteLine(string.Format(string.Format("{{0:0.{0}}}", new string('0', iPlaces)), dValue))

In steps

//Set the value to be shown
decimal dValue = 1.7733222345678M;

//Create number of decimal places
int iPlaces = 6;

//Create a custom format using the correct number of decimal places
string sFormat = string.Format("{{0:0.{0}}}", new string('0', iPlaces));

//Set the resultant string
string sResult = string.Format(sFormat, dValue);

回答3:

See these links for format string help:
http://msdn.microsoft.com/en-us/library/0c899ak8.aspx
http://msdn.microsoft.com/en-us/library/dwhawy9k.aspx

You want this:

Console.WriteLine(Math.Round(1.2345M, x).ToString("F" + x.ToString()));

Additionally, the .ToString call will round for you if needed so you can skip the Math.Round call and just do this:

Console.WriteLine(1.2345M.ToString("F" + x.ToString()));

回答4:

Something like this should handle it:

int x = 3;
string format = "0:0.";
foreach (var i=0; i<x; i++)
    format += "0";
Console.WriteLine(string.Format("{" + format + "}", 1.2M));

回答5:

Method to do that:

private static string FormatDecimal(int places, decimal target)
        {
            string format = "{0:0." + string.Empty.PadLeft(places, '0') + "}";
            return string.Format(format, target); 
        }