input: Write a function to perform a linear search on a given array and return the position of the search item if found, otherwise return -1. The array should be predefined and the search item should be taken as input from the user. If the item is found, print its position, otherwise print "Item not found."
  assert linearSearch('hospital')==1
  assert linearSearch('bookstore')==2
  assert linearSearch('mall')==3
  assert linearSearch('library')==-1
output: def linearSearch(search_item):
      array = ['hospital', 'bookstore', 'mall']
      for i in range(len(array)):
          if array[i] == search_item:
              return i
      return -1