Trying to understand conditions.

i'm trying pick c++ through arduino, , i've gotten point i'm trying use conditions in different applications learn how work.
unfortunately i've come across situation notice knowledge limited, , can't see why, after several google searches, i'm hoping in here might able point me in correct direction.

the application basic one: have 2 led's want flash sequentially, first one, other. should go on indefinitely.

i've gotten work while loop, if loop doesn't work, , keep 1 led flashing, based on value i've set "counter" be.

code: [select]

void setup() {
  // put setup code here, run once:
  pinmode(11, output);
  pinmode(12, output);
}

void loop() {
  // put main code here, run repeatedly:
  int counter = 0;

  if (counter % 2 == 0) { //if "counter" number, run segment:
    digitalwrite(11, high);
    delay(500);
    digitalwrite(11, low);
    delay(500);
    ++counter;
  }
  else {                  //if "counter" isn't number, run this.
    digitalwrite(12, high);
    delay(500);
    digitalwrite(12, low);
    delay(500);
    ++counter;
  }
}

could give me what's wrong thinking and/or code?

at start of each loop, you're putting counter 0.

move counter variable declaration outside of loop it's set 0 once, counting business can proceed.

i'd move counter++ (and correct form, ++ after, not before) single instance outside if else, no need 2 of them. move second delay each in same fashion.

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