input: Write a function to implement a linear search algorithm. 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.
  assert linearSearch([5, 3, 7, 2], 7)==2
  assert linearSearch([1, 2, 3, 4, 5], 6)==-1
  assert linearSearch([10, 20, 30, 40], 30)==2
  assert linearSearch([], 5)==-1
  assert linearSearch([1, 1, 1, 1], 1)==0
output: def linearSearch(arr, value):
      for i in range(len(arr)):
          if arr[i] == value:
              return i
      return -1