input: Write a function to perform a linear search on an array and return the index of the target value if found, or -1 if not found.
  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], 8)==-1
  assert linearSearch([1, 2, 3, 4, 5], 1)==0
  assert linearSearch([10, 20, 30], 30)==2
  assert linearSearch([], 4)==-1
output: def linearSearch(arr, value):
    for i in range(len(arr)):
      if arr[i] == value:
        return i
    return -1