NormalizeDouble seems to do nothing

[Millard Melnyk]

I have no idea why the statement "double dD10th  = 4.1;" would result in the value "4.0999999999999996", but oh well. So I'm trying to round it back to what I originally assigned it, "4.1".

I tried  "double dRnd10th    = NormalizeDouble(dD10th,1);" but that did nothing:

Not sure why 4.1 <> 4.1 (or 4.01 <> 4.01) and not sure what to do about it. 

And why would NormalizeDouble work with d100th but not d10th?

What am I missing?

[AIRAT SAFIN]

Millard Melnyk:

What am I missing?

Web search => normalization is not for such roundings

Real numbers rounding sample

string ROUND_TO_STRING (       double  D   , int LENGTH ) {
return IntegerToString ( (int) round ( D ) ,     LENGTH ) ; }

[Conor Mcnamara]

I think it's because of how the double floating-point numbers are stored in operating systems

maybe it can be hacked that way:

double dRnd10th = MathRound(dD10th * 10.0) / 10.0;

I see 4.1 though if I use NormalizeDouble with Print

double num = 4.0999999999;
double dD10th = NormalizeDouble(num, 1);
Print("TEST: ", dD10th);

[Nikolai Semko]

Millard Melnyk:

I have no idea why the statement "double dD10th  = 4.1;" would result in the value "4.0999999999999996", but oh well. So I'm trying to round it back to what I originally assigned it, "4.1".

I tried  "double dRnd10th    = NormalizeDouble(dD10th,1);" but that did nothing:

Not sure why 4.1 <> 4.1 (or 4.01 <> 4.01) and not sure what to do about it. 

And why would NormalizeDouble work with d100th but not d10th?

What am I missing?

Study this carefully and the questions will disappear:
https://en.wikipedia.org/wiki/IEEE_754

https://en.wikipedia.org/wiki/Double-precision_floating-point_format

You can also play with this calculator to understand this standard:

https://baseconvert.com/ieee-754-floating-point

[Millard Melnyk]

Thanks everyone. What I'm taking away from this is that yeah, it's just a fact of digital life and, no, I don't need to worry about it.

[amrali]

Millard Melnyk #:

Thanks everyone. What I'm taking away from this is that yeah, it's just a fact of digital life and, no, I don't need to worry about it.

https://www.mql5.com/en/forum/440534

Do not rely on the debugger window because it outputs numbers with maximum precision (confusing!!)

To be easy for your eyes, use: 

Print((string)double_value);

[William Roeder]

You used NormalizeDouble, Its use is usually wrong, as it is in your case.

1. Floating point has an infinite number of decimals, it's you were not understanding floating point and that some numbers can't be represented exactly. (like 1/10.)
             Double-precision floating-point format - Wikipedia, the free encyclopedia

   See also The == operand. - MQL4 programming forum (2013)

2. Print out your values to the precision you want with DoubleToString - Conversion Functions - MQL4 Reference.

3. SL/TP (stops) need to be normalized to tick size (not Point) — code fails on non-currencies.
             On 5Digit Broker Stops are only allowed to be placed on full pip values. How to find out in mql? - MQL4 programming forum #10 (2011)

   And abide by the limits Requirements and Limitations in Making Trades - Appendixes - MQL4 Tutorial and that requires understanding floating point equality Can price != price ? - MQL4 programming forum (2012)

4. Open price for pending orders need to be adjusted. On Currencies, Point == TickSize, so you will get the same answer, but it won't work on non-currencies. So do it right.
             Trailing Bar Entry EA - MQL4 programming forum (2013)
             Bid/Ask: (No Need) to use NormalizeDouble in OrderSend - MQL4 programming forum (2012)

5. Lot size must also be adjusted to a multiple of LotStep and check against min and max. If that is not a power of 1/10 then NormalizeDouble is wrong. Do it right.
             (MT4 2013)) (MT5 2022))

6. MathRound() and NormalizeDouble() are rounding in a different way. Make it explicit.
             MT4:NormalizeDouble - MQL5 programming forum (2017)
             How to Normalize - Expert Advisors and Automated Trading - MQL5 programming forum (2017)

7. Prices you get from the terminal are already correct (normalized).

8. PIP, Point, or Tick are all different in general.
             What is a TICK? - MQL4 programming forum (2014)