C# - String formatting: double fixed width

Question

How can I use String.Format in C# so doubles are displayed like this:

Values:

-1.0
1.011
100.155
1000.25
11000.52221

displayed string:

The main point is my width is fixed to 5 characters no matter what. I don't really care how many decimal places are shown to the right. If there are 4 or more numbers to the left of decimal I want everything right of the decimal to be dropped (including the decimal itself).

It seems like something that should be a pretty standard practice. But I'm not having much luck finding an answer that works.

A couple of corrections were made to the display string above, I do want rounding.

Thanks!

"It seems like something that should be a pretty standard practice" - actually no. it's common practice to lineup the decimal point... — Mitch Wheat, Sep 28 '12 at 15:12
Just output it `ToString`, if it's less than 5 characters pad spaces. If it's more than 5 characters, do a special check that it doesn't end with a decimal, and if it does, trim it off. — Chris Sinclair, Sep 28 '12 at 15:13
What if you have a greater than 5 digit number? How does 123456 get handled? Is it 12345? Or is it just out of range anyway? — Chris Sinclair, Sep 28 '12 at 15:14
@HaemEternal Sounds like Harpo just wants digits dropped, no rounding. — Chris Sinclair, Sep 28 '12 at 15:15
This is an interesting puzzle, but the requirements are non-trivial. There certainly appears to be little that is "standard" about this — James Wiseman, Sep 28 '12 at 15:16
I guess "pretty standard practice" may not be right. Bascially I am trying to line these fields up for printing output but some of my data will be large numbers (like 1000.0 or more) and some of my data will be very small numbers like (0.234). They aren't actually the same piece of data, they are just stored using the same type of class and show up on the same output window. — FodderZone, Sep 28 '12 at 15:23
@Harpo, your second entry goes from `1.011` to `1.012`. Is this a typo? — Chris Sinclair, Sep 28 '12 at 15:23

jones · Answer 1 · 2016-01-30T12:06:32.717

3

Usually this rule is applied on exchange market and I develop it as below:

if (number < 1)
   cell.Value = number.ToString("0.00000");
else if (number < 10)
   cell.Value = number.ToString("0.0000");
else if (number < 100)
   cell.Value = number.ToString("00.000");
else if (number < 1000)
   cell.Value = number.ToString("000.00");
else if (number < 10000)
   cell.Value = number.ToString("0000.0");
else if (number < 100000)
   cell.Value = number.ToString("00000");

edited Jan 30 '16 at 12:06

answered Feb 26 '13 at 05:04

jones

317
3
13

1

Perhaps the first `if (number < 0)` should be `if (number < 1)` – robert4 Jan 28 '16 at 08:53
Yes, you are right and I've revised it. thanks a lot! – jones Jan 30 '16 at 12:06

Chris Sinclair · Accepted Answer · 2012-09-28T15:28:06.283

public string FormatNumber(double number)
{
    string stringRepresentation = number.ToString();

    if (stringRepresentation.Length > 5)
        stringRepresentation = stringRepresentation.Substring(0, 5);

    if (stringRepresentation.Length == 5 && stringRepresentation.EndsWith("."))
        stringRepresentation = stringRepresentation.Substring(0, 4);

    return stringRepresentation.PadLeft(5);
}

EDIT: Just realized that this doesn't pad zeros at the end of the decimal if necessary (as in your first example) but should give you the tools to finish it off as you need to.

EDITx2: Given your most recent addition that you intend to have rounding, it gets more complicated. First you have to do a check to see if you will have any decimal places and at what position the decimal is. Then you have to round it to that decimal place, then probably run through the output. Note that depending on your algorithm, you could get some incorrect results where rounding rolls over numbers (for example, -10.9999 could become -11.00 or -11 depending on your implementation)

yes this gives me what I need, and yeah I'll have to add more logic to handle rounding. Thank you though. This will get me where I need to go. — FodderZone, Sep 28 '12 at 15:30

score 1 · Answer 3 · answered Sep 28 '12 at 15:29

Create an extension method on Double if it's going to be used often and in many places.

using System;

public static class DoubleExtensionMethods
{
    public static string FormattedTo5(this double number)
    {
        string numberAsText = number.ToString();

        if (numberAsText.Length > 5)
        {
            numberAsText = numberAsText.Substring(0, 5);
        }

        return numberAsText.TrimEnd('.').PadLeft(5);
    }
}

Useage would then be:

double myDouble = 12345.6789D;

string formattedValue = myDouble.FormattedTo5();

C# - String formatting: double fixed width

3 Answers3

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