• An Pham (12/12) Sep 13 2023 import std.stdio;
• Jonathan M Davis (12/22) Sep 13 2023 The nature of floating point numbers is such that there a bunch of value...
• Basile B. (5/18) Sep 13 2023 Classic question. The float literal `6394763.345f` is not

An Pham <home home.com> writes:

import std.stdio;

     void main()
     {
         float f = 6394763.345f;
     	
         import std.format : sformat;

         char[80] vBuffer = void;
         writeln("6394763.345 = ", sformat(vBuffer[], "%.4f", f));
     	
     }

Output
6394763.345 = 6394763.5000

Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:

On Wednesday, September 13, 2023 9:23:48 PM MDT An Pham via Digitalmars-d-
learn wrote:
 import std.stdio;

      void main()
      {
          float f = 6394763.345f;

          import std.format : sformat;

          char[80] vBuffer = void;
          writeln("6394763.345 = ", sformat(vBuffer[], "%.4f", f));

      }

 Output
 6394763.345 = 6394763.5000

The nature of floating point numbers is such that there a bunch of values
that they can't actually represent, and they get rounded pretty easily
depending on the exact numbers involved. So, in general, you shouldn't
expect floating point numbers to be exact. You will generally do better with
increased precision though, and in this case, it looks like your number will
stay the same if you use double or real instead of float.

I would suggest that you watch this video from dconf 2016 which discusses
floating point values:

https://www.youtube.com/watch?v=YEUAUnamQiA

- Jonathan M Davis

Basile B. <b2.temp gmx.com> writes:

On Thursday, 14 September 2023 at 03:23:48 UTC, An Pham wrote:
 import std.stdio;

     void main()
     {
         float f = 6394763.345f;
     	
         import std.format : sformat;

         char[80] vBuffer = void;
         writeln("6394763.345 = ", sformat(vBuffer[], "%.4f", 
 f));
     	
     }

 Output
 6394763.345 = 6394763.5000

Classic question. The float literal `6394763.345f` is not 
representable as IEEE-754 floating point number.

Try https://www.h-schmidt.net/FloatConverter/IEEE754.html for a 
short introduction to the issue.