#First we assign a value to a variable.
x = 4
#Now we see that we can reuse it
x
y
#Uh oh, looks like we didn't define our variable.
#so we assign something to it.
y = 15 + 8
y
#What if we assign a variable a new value?
x = 20
x
#x now refers to the value 20 and not the value 4.
#We can use more than one variable in an expression.
y
y = x - 2
y
#So now y refers to a value that depends on the value that x referred to.
#What if we change the value of x?
x = 100
y
#This means that when we assign y to refer to a value that depends on x, we don't tie the variables together, the value that y refers to depends only on the value that x referred to *at that point*.
y = x + 2
y
#What if we get y to refer to a value that depends on the value it refers to?
#Like: draw on the board.
#Does this even make sense? In math it doesn't.
#But math equality is different then assignment.








#Recall that assignment has two steps: First we evaluate the RHS, and then we assign that location to the LHS.
#So what do we think will happen?
y
y = y + 1
y
#now let's draw what happened on the board.

#let's make sure we're clear on the distinction between evaluation and assignment.
x
x + 18
x
x = x + 18
x
#in the first case, we threw away the memory address of the value, but in the second case we kept it.
#what if we're lazy? Can define multiple assignments at one.
a, b= 9,17
a
b


#another distinction between math and assignment.
sum = x + y
sum
#everything's fine.
#in math, the following would mean the same thing as the assignment above.
x+y = sum
#but instead we get a giant mess.
#back to slides.