Unexplainable int behavior in encoder/LED project

Question

I am trying to use a rotary encoder to cycle through the brightest versions of R, G & B. And it works! Red goes to blue just fine. Then G happens. For some reason, the int for green goes completely haywire. And it does this the same way on two Arduinos.

So my question is this: why would two, identically assigned variables treat ++ completely differently? After hours (and hours and hours) of looking, I'm completely out of possible answers.

#include <Encoder.h>
#include <FastLED.h>
/* Encoder */
Encoder myEnc(2, 3);
const int swPin = 4 ;
long oldPosition = -999;
/* LEDs */
#define LED_PIN 7
#define NUM_LEDS 150
CRGB leds[NUM_LEDS];
/* RGB Loop */
volatile int cycle = 1;
volatile int brightness = 0;
volatile int r = 127;
volatile int g = 0;
volatile int b = 0;
void setup() {
 pinMode(swPin, INPUT);
 Serial.begin(9600);
 FastLED.addLeds<WS2812, LED_PIN, GRB>(leds, NUM_LEDS);
}
void loop() {
 // Read from rotary encoder.
 long newPosition = myEnc.read();
 if (newPosition != oldPosition) {
 oldPosition = newPosition;
 Serial.println(newPosition); /* Sends elsewhere */
 }
 /* Will eventually move this inside the above if 
 * statement so the color shift is controlled by
 * a rotary encoder. Down here for debugging. 
 */
 delay(50);
 updateColor( );
}
void updateColor( ) {
 Serial.println(" "); // For readability. 
 if ( brightness >= 127 ) {
 brightness = 1;
 if ( cycle > 6 ) {
 cycle = 1;
 } else {
 cycle++;
 }
 } else {
 brightness++;
 }
 if ( cycle == 1) {
 b++;
 }
 else if ( cycle == 2) { /* rb --> b */
 r--;
 }
 else if ( cycle == 3) { /* b --> bg */
 g++;
 }
 else if ( cycle == 4) { /* bg --> g */
 b--;
 }
 else if ( cycle == 5) { /* g --> rg */
 r++;
 }
 else if ( cycle == 6) { /* g --> rg */
 g--;
 }
 else {
 Serial.print("==================== ");
 }
 /* Debugging */
 Serial.print("brightness:");
 Serial.print(brightness);
 Serial.print(" cycle:");
 Serial.print(cycle);
 Serial.print(" r:");
 Serial.print(r);
 Serial.print(" g:");
 Serial.print(g); // goes completely bonkers
 Serial.print(" b:");
 Serial.print(b);
 Serial.println(" ");
 for (int i = 0; i <= NUM_LEDS; i++) {
 leds[i].setRGB( r, g, b );
 }
 FastLED.show();
}

spits out the following in the serial monitor :

brightness:1 cycle:1 r:127 g:0 b:1 
brightness:2 cycle:1 r:127 g:127 b:2 
brightness:3 cycle:1 r:127 g:32639 b:3 
brightness:4 cycle:1 r:127 g:32639 b:4 
brightness:5 cycle:1 r:127 g:32639 b:5 
brightness:6 cycle:1 r:127 g:32639 b:6 

Red and blue are doing exactly what I want. Green is off on Mars.

Any/all help would be enormously appreciated. Thanks in advance.

• Jot: 127 = 0x7F, 32639 = 0x7F7F.
• Tarick Welling: I can't yet comment so therefore here. Could you try casting the rgb printouts to uint8_t? It could be that it goes out of bounds or something? I don't see anything wrong with the code so maybe it could be that some pointer is changing the value of g?
• DataFiddler: I do not see a relation between the encoder and the r,g,b values. Or between the encoder and your rgb problem. BTW: rgb values are byte, not int
• Jot: laffan, we don't see the problem. It could be a compiler or optimization bug (not likely, but it is possible) or a bug in a library that overwrites memory. You have to try a number of things. Start with an example, and slowly change that in the direction of your sketch. The setRGB is a inline function that has uint8_t as parameters. I think there is no need to make the variables volatile.
• laffan: Thank you all! @Jot I think you're on to something. I'm not sure what you're on to, but that at least explains the number. Looks like I need to learn some more about hexidecimals. And good to know re: that variable volatility (I was grasping at straws.) Tarik Welling - I'm afraid this hobbiest hasn't gotten to pointers yet, but I'll take a look. DataFiddler - The new/old position thing is the rotary encoder part (see comments) which works, incredibly. Thanks for the byte tip.

Answer 1

Here:

CRGB leds[NUM_LEDS];

you are defining an array of NUM_LEDS objects of the CRGB type. Valid indices for this array range from 0 to NUM_LEDS-1.

Here:

for (int i = 0; i <= NUM_LEDS; i++) {
 leds[i].setRGB( r, g, b );
}

you are accessing the array elements at indices 0 to NUM_LEDS. The last iteration is an out-of-bounds access, which is causing memory corruption. You should instead write

for (int i = 0; i < NUM_LEDS; i++) ...

• laffan: Thank you so much @edgar-bonet - I don't think I ever would have figured that out.