/*
  // https://forum.arduino.cc/t/binary-counter-led-project-issue/1438696

  You stated you would be counting to fifteen:
  [quote="belerand317, post:1, topic:1438696"]
  4 LEDs (this part is done and working correctly), and then to write a program that will count from 0-15
  [/quote]

  But your code counts to eight (bits, I think) which would be equal to `2 ^ 8 = 256`... and the full code seems a bit too much for the task.

  Try coding in steps... using your idea: Count from zero to fifteen.  Represent that count in Binary.  Show the count using LEDs.  Make each count take one second.

  Step 1. Write a sketch (program) that uses `loop()` to count from zero to fifteen.
*/
```
byte counter, maxCount = 15; // variables for counting and maximum

void setup() {
  Serial.begin(115200); // start serial monitor
}

void loop() {
  countup();
}

void countup() {
  if (counter > maxCount) // verify counter is below maximum...
    while (1) {}; // stop the program here
  Serial.println(counter); // all is well, print the value
  counter++; // increase counter
}
```
/*
  Step 2. Control timing for each count (for example; at one second intervals...
*/
```
byte counter, maxCount = 15; // variables for counting and maximum
bool shownext; // flag to indicate when to show the count
unsigned long timer, timeout = 1000; // timer variables

void setup() {
  Serial.begin(115200); // start serial monitor
}

void loop() {
  timecount(); // call function to tell when to show the count
  if (shownext) { // if timecount() flag indicates it is time...
    shownext = false; // ... reset flag and...
    countup(); // ... call the function to show the count
  }
}

void timecount() {
  if (millis() - timer >= timeout) { // if timeout is overrun...
    timer = millis(); // ... store millis() "now" time
    shownext = true; // ... call the counting function
  }
}

void countup() {
  if (counter > maxCount) // verify counter is below maximum...
    while (1) {}; // stop the program here
  Serial.println(counter); // all is well, print the value
  counter++; // increase counter
}
```
/*
  Step 3. Count from 0 to 15 and translate base - 10 to base - 2
*/
```
byte counter, maxCount = 15; // variables for counting and maximum
bool shownext; // flag to indicate when to show the count
unsigned long timer, timeout = 100; // timer variables

void setup() {
  Serial.begin(115200); // start serial monitor
}

void loop() {
  timecount(); // call function to tell when to show the count
  if (shownext) { // if timecount() flag indicates it is time...
    shownext = false; // ... reset flag and...
    countup(); // ... call the function to show the count
  }
}

void timecount() {
  if (millis() - timer >= timeout) { // if timeout is overrun...
    timer = millis(); // .. store millis() "now" time
    shownext = true; // ... call the countup function
  }
}

void countup() {
  if (counter > maxCount) // verify counter is below maximum...
    while (1) {}; // ... counter is above max, stop the program
  if (counter < 10)
    Serial.print(0);
  Serial.print(counter); // all is well, print the value
  Serial.print(" = ");
  dectobin(counter); // call the decimal to binary function
  counter++; // increase counter
}

void dectobin(byte decimal) { // receive the counter value
  byte binary[4], bits; // four bits
  while (decimal) { // greater than zero means more bits
    Serial.print(decimal % 2);
    // binary[bits++] = decimal % 2; // collect bits LSB to MSB
    decimal /= 2; // divide by base 2
  }
  bits = 0; // reset bit number
  for (byte i = 0; i < 4; i++) { // count four bits
    Serial.print(binary[3 - i]); // invert bit order MSB to LSB
  }
  Serial.println(); // next line
}
```