//main variable for storing solution.
var ears;

/**
* Sets collector variable to 0 and calls the recursion function.
* @param {number} amountOfBunnies - The amount of bunnies that need to have ears counted.
* @return {(number | string)} - Return either the solution or error message if parameters were invalid.
*/
function recursiveCalculateEars(amountOfBunnies) {
  if (typeof amountOfBunnies == 'number'){
    ears = 0;
    return recursion(amountOfBunnies);
  } else {
    return 'Invalid parameters.';
  }
  /**
  * Main recursion function, recalls itself untill i == 0.
  * @param {number} i
  * @return {number} - The total amount of ears counted according to the variable ears.
  */
  function recursion(i){
    if (i > 0){
      ears += 2;
      return recursion(i - 1);
    } else if(i < 0){
      ears -= 2;
      return recursion(i + 1);
    } else if(i == 0){
      return ears;
    }
  }
}
/**
* Iteratively calculates amount of bunny ears using a for loop.
* @param {number} amountOfBunnies - The amount of bunnies to be calculated.
* @return {(number | string)} - Return either the solution or error message if parameters were invalid.
*/
function iterativeCalculateEars(amountOfBunnies){
  if (typeof amountOfBunnies == 'number'){
    ears = 0;
    if (amountOfBunnies > 0){
      for (var i = amountOfBunnies; i > 0; i--){
        ears += 2;
      }
    }else if (amountOfBunnies < 0){
      for (var i = amountOfBunnies; i < 0; i++){
        ears -= 2;
      }
    }
    return ears;
  } else {
    return 'Invalid parameters.'
  }
}