input: def linearSearch(arr, value):
      """ Create a linear search algorithm that takes an array and a value to search for.
      The function should return the index of the value if found, or -1 if not.
      >>> linearSearch([5, 3, 7, 2], 7)
      2
      >>> linearSearch([5, 3, 7, 2], 8)
      -1
      """
output:     for i in range(len(arr)):
          if arr[i] == value:
              return i
      return -1