input: Write a function to create an algorithm 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. If the given array is empty then return -1.
  assert linearSearch([5, 3, 7, 2], 7)==2
  assert linearSearch([5, 3, 7, 2], 2)==3
  assert linearSearch([5, 3, 7, 2], 10)==-1
  assert linearSearch([], 7)==-1
output: def linearSearch(arr, value):
      if not arr:
          return -1
      for i in range(len(arr)):
          if arr[i] == value:
              return i
      return -1