Simple LEDs and Serial sketch - weird bug?

Projects Programming
1

I'm a newbie with arduino, but slightly more experienced with programming and circuits.

I was trying a simple program -
9 LEDs connected to 9 output pins (2-10), each connected in series a to 330ohm resistor.
The sketch selects 2 random pins, and causes the corresponding LEDs to blink twice.

The program worked great.

I then added a serial communication to see in the monitor what pins are selected (I basically added a println to print values of integers i and j):
Program goes crazy. LEDs stop behaving as before.

what am I missing?!
(see attached ino file)

Thanks.

Leds_and_Serial.ino (870 Bytes)

2

Easy, when you print the values, you have the following syntax:

Serial.println(i,j);

It should be:

Serial.print(i);
Serial.print(", ");
Serial.println(j);

That should fix it.

3

Also, I don't know if this changes anything, but you don't set a seed for the random function.

See:

https://www.arduino.cc/en/Reference/RandomSeed

5 
  i,j=random(0,9);                // generate 2 random numbers between 0 and 8, to select 2 pins

That is NOT what that code does. Only Kernighan and Ritchie are allowed to invent syntax. The rest of us have to use what they invented.

6

Thanks Everyone. It works OK now.

BTW, PaulS, I never said I wasn't Kernighan or Ritchie..... Obiously Joker54 is not my legal name.

7

I never said I wasn't Kernighan or Ritchie.

I'm Spartacus !