"""
Author:Nguyễn Manh Trung
Date: 24/09/2021
Problem:
  Assume that the variable data refers to the string "myprogram.exe". Write the
expressions that perform the following tasks:
a. Extract the substring "gram" from data.
b. Truncate the extension ".exe" from data.
c. Extract the character at the middle position from data.
Solution:
    > data = "gram"
    > data [5:9]
    'gram'
    > data [-4]
    '.exe'
    > data [6]
    'r'
    ....
"""