Can't figure how to print 2 decimals correctly(SOLVED)

Projects Programming
1

Real simple: I print a float and I am expecting to get the 2 decimals correctly and disregard the rest.
instead I get a round up version. Right?
Code is
Serial.println (Uptime_Hrs, 2);
Serial.println (Uptime_Hrs, 4);

Gets me:
0.01
0.0075

I would want the top number not to change to one hundredth till the actual value exceeds 0.01

Please help, Thanks

2

Please post code.

3

That is how Serial.print() works.

4

f = 0.0099
f * 100 = 0.99
floor( f * 100 ) = 0.00
floor( f * 100 ) / 100 = 0.00

f = 0.0100
f * 100 = 1.00
floor( f * 100 ) = 1.00
floor( f * 100 ) / 100 = 0.01

5

Try:
Serial.println (Uptime_Hrs-0.005, 2);
This will un-do the 'round to the nearest 0.01' that print does.

6

John
thanks that worked, but the first few readings are weird. Negative Zero....?
I can't deliver this project like this, I would need a 0.00

Look
-0.00
0.0039
Downtime Seconds: 15
CumulatedUpTimeSec: 14 DOWN_TimeSec 0

30
-0.00
0.0042
Downtime Seconds: 15
CumulatedUpTimeSec: 15 DOWN_TimeSec 0

31
-0.00
0.0044
Downtime Seconds: 15
CumulatedUpTimeSec: 16 DOWN_TimeSec 0

32
-0.00
0.0047
Downtime Seconds: 15
CumulatedUpTimeSec: 17 DOWN_TimeSec 0

33
0.00
0.0050
Downtime Seconds: 15
CumulatedUpTimeSec: 18 DOWN_TimeSec 0

34
0.00
0.0053

7

No, a negative number, closer to zero than -0.005.

8

I kinda figured something, not elegant but the best I got.

 String str2 = String(Uptime_Hrs, 4);
  Serial.print ("Uptime_Hrs-string Original : "); Serial.println (str2);
  int str2_LENGHT = str2.length();
  
  Serial.print ("str2_LENGHT: "); Serial.println (str2_LENGHT);
  str2.remove(str2_LENGHT-2, 2);

This actually works.
I don't know why the String(Uptime_Hrs, 2); still does the rounding.
So I had to generate a 6 digit string...etc

Hope others will figure something easier...
Thanks
MITCH

9

Did you try floor( f * 100 ) / 100 as suggested in reply #4 ?

10

Sorry. Try this:

  if (Uptime_Hrs >= 0.005)
    Serial.println (Uptime_Hrs-0.005, 2);
  else
    Serial.println (0.00, 2);
11

Thanks a lot everyone. Problem Solved

12

John,
I just made it an absolute number, it works.
Serial.println (abs (Uptime_Hrs-0.005), 2);