input: Write a function to perform a linear search. The function 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. If the array is empty, the function should return -1.
  assert linearSearch([5, 3, 7, 2], 7) == 2
  assert linearSearch([5, 3, 2, 8], 4) == -1
  assert linearSearch([], 10) == -1
  assert linearSearch([1, 2, 3, 4], 3) == 2
output: def linearSearch(arr, value):
      if not arr:
          return -1
      for i in range(len(arr)):
          if arr[i] == value:
              return i
      return -1