'''  Purpose:  introduce variable usage, assignment and hand-checking of code.
'''

n = 17
print( "n =", n ) 

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

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

u = t // 2
print( "u =", u ) 
u = 1
print( "u =", u ) # u is 1
v = u - n   # 1 - 17 = -16
print( "v =", v )

u = -5
print( "u =", u ) 

print( "v =", v )

a = v

print( "a =", a )

# v = u - n had a value (1-17 = -16)
# the value of v doesn't change if u / n get changed unless you reassign v after u is changed
# v is currently - 16
# u = 5
# u gets changed but v isn't! u = 5 and v = -16 at this point
# unless we do
# v = u - n # AGAIN because now we have a different value for u! 5 - 17 = -12
# now v = -12
# The value for v is NOW changed since we reassigned it!

# IMPORTANT
    # So variables retain the last value we assigned them!
    # The value of variables change if we reassign them!

# THIS WILL NOT WORK:
# z = x + y # You need to define/assign your variables before you use them in expressions!
# x = 2
# y = 4