Pfthb

First of all, I know the problem with the code and how to get it to work. I'm mainly looking for an explanation why my output is what it is.

The following piece of code replicates the behaviour:

void setup() 
 Serial.begin(9600);


void loop() 
 Serial.println("start");
 for(int i = 0; i < 70000; i++) 
 if((i % 2000) == 0)
 Serial.println(i);
 

Obviously the for loop will run forever because i will overflow at 32,767. I would expect it to overflow and print -32000.

Expected| Actually printed
0 | 0 
2000 | 2000 
4000 | 4000 
... | ... 
30000 | 30000 
32000 | 32000 
-32000 | 33536 
-30000 | 35536 

It looks like it prints the actual iterations, since if you overflow and count to -32000 you would have 33536 iterations, but I can't figure out how it's able to print the 33536.

The same thing happens every 65536 iterations:

95536 | 161072 | 226608 | 292144 | 357680
97536 | 163072 | 228608 | 294144 | 359680
99072 | 164608 | 230144 | 295680 | 361216
101072 | 166608 | 232144 | 297680 | 363216

EDIT

When I change the loop to add 10.000 every iteration and only print every 1.000.000 to speed it up the Arduino crashes (or at least, the prints stop) at '2.147.000.000'. Which seems to point to the 32-bit idea of svtag**

EDIT2

The edits I made for the 2.147.000.000-check:

void loop() 
 Serial.println("start");
 for(int i = 0; i < 70000; i+=10000) 
 if((i % 1000000) == 0)
 Serial.println(i);
 

They work in the same trend with the previous example, printing 0, 1000000, 2000000,...

However, when I update the AVR package from 1.6.17 to the latest 1.6.23 I get only 0's. The original example (% 2000 & i++) still gives the same output.

The compiler may have automatically casted the i to usigned int when you are doing the println or the value is going to the wrong overload. Try using Serial.println((int)i);