How to convert a big float into a string with commas without rounding

Question

I have a large float that I want to convert into a string with commas without rounding.

Here is what I have:

String.Format("{0:#,###}", val);

This turns 17154177 into 17,154,180 I would like to keep the commas but not round at the end using c#.

`String.Format` is not a native JavaScript method on the `String` object. Where are you getting that from? You could try [`toLocaleString()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toLocaleString). — chipit24, Jul 02 '20 at 21:32
Does this answer your question? [prevent rounding of decimals when using currency string format](https://stackoverflow.com/questions/6042262/prevent-rounding-of-decimals-when-using-currency-string-format) — AndrewL64, Jul 02 '20 at 21:35
This smells like a floating point rounding problem, not a string conversion problem. Single-precision floating point values are only precise to [~6 significant digits](https://stackoverflow.com/a/50492868/3791245), but you want precision out to 8 digits. Consider using `decimal` instead of `float`. — Sean Skelly, Jul 02 '20 at 21:55

Rod Talingting · Answer 1 · 2020-07-02T22:05:41.913

1

Change your data type to decimal (28-29 significant digits) to have higher precision compared to float (7 digits).

Or you can change it to var. It will let the compiler figure out the best data type to use.

var number = 17154177;
Console.WriteLine(String.Format("{0:#,###}", number));

See this fiddler link, working code

edited Jul 02 '20 at 22:05

answered Jul 02 '20 at 21:37

Rod Talingting

943
1
15
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Make that number you used into a float first and it does not work – TheProgrammer Jul 02 '20 at 21:40
You are right. You can also change it to decimal to make it 128 bits compare to float which only has 32 bits (7 digits). I updated my dotnet fiddle – Rod Talingting Jul 02 '20 at 21:54
1

I ended changing the datatype to double as soon as it came into the application from DB side – TheProgrammer Jul 02 '20 at 22:30
What is the database datatype of "17154177"? – Rod Talingting Jul 02 '20 at 22:35

diogo.silva · Answer 2 · 2020-07-02T21:54:16.457

1

This may be what you're looking for

using System;

class MainClass {
  public static void Main (string[] args) {
    float original = 17154177;

    // 1. Convert the number to a string
    string value = original.ToString("R");

    // 2. Reverse the string
    string reversed = Reverse(value);

    // 3. Add the comma on each third number, backwards
    string formatted = "";
    for(int i = 0; i < reversed.Length; i++) {
      if ((i+1) % 3 == 0) {
        formatted += reversed[i] + ",";
      } else {
        formatted += reversed[i];
      }
    }

    // 4. Reverse it back to the original order
    formatted = Reverse(formatted);

    Console.WriteLine (formatted);
  }

  /* Reverses a string */
  public static string Reverse(string text)
  {
    char[] cArray = text.ToCharArray();
    string reverse = String.Empty;
    for (int i = cArray.Length - 1; i > -1; i--)
    {
        reverse += cArray[i];
    }
    return reverse;
  }
}

I got the reverse method from this question.

edited Jul 02 '20 at 21:54

answered Jul 02 '20 at 21:45

diogo.silva

448
4
13

I dont think this works well with floats, I got ,70+,E81,451,7.1 as the result – TheProgrammer Jul 02 '20 at 21:52
Let me check and see what I can do – diogo.silva Jul 02 '20 at 21:52
I fixed the compatibility with floats. Just needed to add "R" inside `ToString` – diogo.silva Jul 02 '20 at 21:54
You can see it working here: https://repl.it/repls/OrganicFlusteredText#main.cs – diogo.silva Jul 02 '20 at 21:56
In this example, it rounds it down by 1 number – TheProgrammer Jul 02 '20 at 22:00
C# seems to still be rounding the last digit. Let me check once more and see if I can fix it – diogo.silva Jul 02 '20 at 22:03
Seems to be working with `double`. Do you need the number to be a float? – diogo.silva Jul 02 '20 at 22:06
The value comes in as a float from the database I will try to convert to see – TheProgrammer Jul 02 '20 at 22:07
If you could find a way to get the value from DB directly as a string, you could format it directly by using the comma concatenation I wrote – diogo.silva Jul 02 '20 at 22:11
Check this out: https://stackoverflow.com/a/3715741/8469219 – diogo.silva Jul 02 '20 at 22:16
1

I ended up changing value to double as soon as it came in from DB and it worked with the formatting i have – TheProgrammer Jul 02 '20 at 22:31
Yup. The problem in general was due to convertions. Glad you got it solved! – diogo.silva Jul 02 '20 at 22:32

How to convert a big float into a string with commas without rounding

2 Answers2