input: Write a function to create an algorithm in Python for a linear search. The algorithm should take in an array and a value to search for, and return the index of the value if it is found, or -1 if it is not.
  assert linearSearch([5, 3, 7, 2], 7) == 2
  assert linearSearch([5, 3, 7, 2], 9) == -1
  assert linearSearch([1, 2, 3, 4, 5], 5) == 4
  assert linearSearch([1, 2, 3, 4, 5], 6) == -1
  assert linearSearch([], 1) == -1
output: def linearSearch(arr, value):
      for i in range(len(arr)):
          if arr[i] == value:
              return i
      return -1