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Re: C++ (and some C) quiz questions

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Ben <ben.usenet@bsb.me.uk> writes:

> Juha Nieminen <nospam@thanks.invalid> writes:
>
>> Christian Gollwitzer <auriocus@gmx.de> wrote:
>>
>>>> Re #5, I guess that the problem with
>>>>
>>>>   long double value = 0.1;
>>>>
>>>> ... is that when `long double` doesn't have the same representation as
>>>> `double`, one may get a less precise value than with
>>>>
>>>>   long double value = 0.1L;
>>>>
>>>> Is that it?
>>>
>>> That's how I see it.  0.1 is a double constant and since 1/10 can't be
>>> represented exactly in binary (assuming binary floats), the value in
>>> "value" is not the closes approximation to 0.1 possible, which is 0.1L.
>>
>> It's easy to make such mistakes, and not just in variable initialization,
>> but also pretty much anywhere where a literal is used, like:
>>
>>     x = y * 0.1; // If x and y are long double, precision is lost
>
>   7.4 Usual arithmetic conversions
>
>   (1.2) ? If either operand is of type long double, the other shall be
>           converted to long double.

But that doesn't change the problem of potential loss of
precision, because the representation (and hence the particular
value) of the constant 0.1 is chosen before that value is
converted to long double.  The constant 0.1, being of type
double, doesn't have to have less precision than 0.1L, but
certainly it can.

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Thread

C++ (and some C) quiz questions Juha Nieminen <nospam@thanks.invalid> - 2022-05-16 11:21 +0000
  Re: C++ (and some C) quiz questions Paavo Helde <eesnimi@osa.pri.ee> - 2022-05-16 17:35 +0300
    Re: C++ (and some C) quiz questions Juha Nieminen <nospam@thanks.invalid> - 2022-05-16 16:13 +0000
  Re: C++ (and some C) quiz questions Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-16 10:49 -0700
  Re: C++ (and some C) quiz questions Christian Gollwitzer <auriocus@gmx.de> - 2022-05-16 20:02 +0200
    Re: C++ (and some C) quiz questions "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-16 20:51 +0200
      Re: C++ (and some C) quiz questions Christian Gollwitzer <auriocus@gmx.de> - 2022-05-16 20:59 +0200
        Re: C++ (and some C) quiz questions Manfred <noname@add.invalid> - 2022-05-16 21:55 +0200
          Re: C++ (and some C) quiz questions Christian Gollwitzer <auriocus@gmx.de> - 2022-05-16 22:09 +0200
            Re: C++ (and some C) quiz questions Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-16 13:47 -0700
              Re: C++ (and some C) quiz questions Ben <ben.usenet@bsb.me.uk> - 2022-05-16 22:19 +0100
                Re: C++ (and some C) quiz questions Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-05-16 14:52 -0700
                Re: C++ (and some C) quiz questions Ben <ben.usenet@bsb.me.uk> - 2022-05-16 22:57 +0100
            Re: C++ (and some C) quiz questions Paavo Helde <eesnimi@osa.pri.ee> - 2022-05-17 00:54 +0300
              Re: C++ (and some C) quiz questions Ben <ben.usenet@bsb.me.uk> - 2022-05-17 00:34 +0100
                Re: C++ (and some C) quiz questions Christian Gollwitzer <auriocus@gmx.de> - 2022-05-17 08:24 +0200
                Re: C++ (and some C) quiz questions Juha Nieminen <nospam@thanks.invalid> - 2022-05-17 08:21 +0000
                Re: C++ (and some C) quiz questions Ben <ben.usenet@bsb.me.uk> - 2022-05-17 11:06 +0100
        Re: C++ (and some C) quiz questions Juha Nieminen <nospam@thanks.invalid> - 2022-05-17 04:41 +0000
          Re: C++ (and some C) quiz questions Ben <ben.usenet@bsb.me.uk> - 2022-05-17 11:12 +0100
            Re: C++ (and some C) quiz questions Paavo Helde <eesnimi@osa.pri.ee> - 2022-05-17 14:37 +0300
              Re: C++ (and some C) quiz questions Ben <ben.usenet@bsb.me.uk> - 2022-05-17 14:31 +0100
            Re: C++ (and some C) quiz questions Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-05-17 04:53 -0700
              Re: C++ (and some C) quiz questions Juha Nieminen <nospam@thanks.invalid> - 2022-05-18 04:40 +0000
                Re: C++ (and some C) quiz questions Manfred <noname@add.invalid> - 2022-05-18 13:29 +0200
                Re: C++ (and some C) quiz questions Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-05-18 06:57 -0700
                Re: C++ (and some C) quiz questions Paavo Helde <eesnimi@osa.pri.ee> - 2022-05-18 17:37 +0300
                Re: C++ (and some C) quiz questions Juha Nieminen <nospam@thanks.invalid> - 2022-05-19 14:43 +0000
                Re: C++ (and some C) quiz questions Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-05-19 08:21 -0700
                Re: C++ (and some C) quiz questions Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-05-18 06:01 -0700

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