'''  Purpose:  introduce variable usage, assignment and hand-checking of code.
'''
# wouldn't it be fun if we could change up each run of this program?
# we would have to get input from the user
# new function!!: reply = input("prompt") prompt is a string usually, in quotations
# GOTCHA: the input() function ALWAYS hands back a STRING containing what has been typed by the user, even if it's all numeric
# we'll talk about how to get numbers from strings!
n = 191
print( "n =", n ) 

s = 2 * n 
print( "s =", s )

t = s + 4
print( "t =", t ) 

u = t // 2
print( "u =", u ) 

v = u - n
print( "v =", v )

u = -5
print( "u =", u ) 
# v = 3
print( "v =", v )

# only the things on the left are updated, and variables don't track where they came from
# this is a GOTCHA! remember how to walk through line by line and track your variables, it's very helpful in debugging
# u does not care that it was calculated from t