input: Write a function to perform a linear search on an array and return the index of the value if it is found, or -1 if it is not. If the given array is empty, then return -1.
  def linearSearch(arr, value):
    for i in range(len(arr)):
      if arr[i] == value:
        return i  # value found, return index
    return -1  # value not found
  
  assert linearSearch([5, 3, 7, 2], 7) == 2
  assert linearSearch([5, 3, 7, 2], 10) == -1
  assert linearSearch([], 7) == -1
output: def linearSearch(arr, value):
    for i in range(len(arr)):
      if arr[i] == value:
        return i
    return -1