Introductory Programming
Fall 2006

For today, you should have:

1) Finished Homework 1.

2) Prepared for an evaluation.


Today:

1) Evaluation 1

2) updating variables

3) if and for statements


For next Tuesday you should:

1) Read Chapter 2


Updating variables
------------------

What do these lines of code do?

x = 5
x = x + 1

The second one looks funny, because in math it would be
an equation with no solutions.

But as an assignment statement, it makes perfect sense.

Remember that the order of events is

1) evaluate the right hand side.

2) create the new variable if necessary.

3) assign the value of the RHS to the variable.

So what happens if you try this

y = y + 1


Simultaneous updates
--------------------

Suppose we have two variables, a and b, and we want to
update them both.

For example, imagine two car lots, with a cars on Lot A
and b cars on Lot B.

Each day, 3% of the cars from Lot A go to Lot B
and       5% of the cars from Lot B go to Lot A

Write a few lines of code that compute the new values
of a and b based on the old values.









Store your code in a file named update.m

Now start with the initial values a = 200, b = 100

And call your script 10-20 times (up-arrow, return)

What happens to the values of a and b?


if statements
-------------

n = n + 1
if n < 10
    update
end


for loops
---------

for i=1:10
    update
end


fprintf
-------

Formatted printing (ugly feature!)

fprintf('%f\t%f\n', a, b)