There are no stupid questions you say? HA! how about:
I'm trying to count down from 15 to 0 in a loop.
for (byte counter=15; counter>=0; counter--)
does not turn around at 0, wraps around to 255 and continues to decrement ("...4, 3, 2, 0, 255, 254...")
Modifying to:
for (byte counter=15; counter>0; counter--)
turns around, but does not output 0: "...4, 3, 2, 1, 1, 15..." (no delay after the second 1))
Any help appreciated.
Use char instead of byte.
try this:
for (signed char counter=15; counter>=0; counter--)
[\code]
sorry, here's the whole code snippet:
{
for (byte counter=seqLength; counter>=0; counter--) //--DAMMIT. if counter>=0, does not turn around at 0, wraps around to 255 and continues to decrement
//if counter>0, turns around but does not output 0: "4, 3, 2, 1, 1, 15..." (no delay after the second 1))
{
displayBinary(counter);
Serial.println(counter);
delay(seqSpeed);
}
}
seqLength and seqSpeed are variables; displayBinary is a routine to convert output to binary on 4 digital pins.
Right? So change byte into a signed char like I suggested and try it.
Also start using the code tags to post your code.
Two options, do as the two above say.
Or, when you are 100% convinced the initial value is lower as 255 make it
for (byte counter=15; counter != 255; counter--)
signed char seems to work, thanks!
i'm still getting an extra value output at the turnaround, and something similar in countUp function
countdown: 4, 3, 2, 1, 0, 1, 15, 14 (second 1 does not trigger delay)
countup: 13, 14, 15, 0, 0, 1, 2, 3 (second 0 no delay)
not a problem, i think, but makes me curious
Post your whole code using the tags, and we might be able to spot it.
found it (errant debugging println i forgot to comment out). thanks again, all, this is a foreign land to me...
Id like to write an explanation of binary arithmetic using car odometers as a metaphor
Could someone please explain or point to an explanation of the reason why "signed char" must be used instead of "byte" ?
A byte is an unsigned type so it can't become negative. So 0 - 1 will roll around to the greatest value 255. A signed char can be negative but the greatest value is 127.
So instead for checking:
for(byte i = 10; i < 0; i--) //will never stop because i can not become negative
You can use the fact it will just roll around and check for
for(byte i = 10; i != 255; i--) //will happen because i will become 255 after subtracting 1 from 0
Ok, got it, any data type that handles negative values will work. Signed char was chosen in this case because the value "counter" is not exceeding 127. Or, use this: i != 255; with byte, so i will never be 255. Thank you very much for the explanation septillion. +1 karma