The list of problems for this week's exam is at: 

http://www.cs.indiana.edu/classes/a201-dger/sum2009/weekThree.txt

Today we want to discuss problems 3, 6, 5. 

Tomorrow we want to work on 1, 2, 4 -- to be ready for Friday. 

I'll post the code we develop in class right here. 

Here's how I would start on the Vending Machine: 

+-----------------------------------------------------------
| print "Welcome to the Vending Machine!"
| 
| line = raw_input("enter> ")
+-----------------------------------------------------------

Next we can establish a communication loop: 

+-----------------------------------------------------------
| print "Welcome to the Vending Machine!"
| 
| line = raw_input("enter> ")
| 
| while line != "done":
|     line = raw_input("enter> ")
| 
| print "Thanks for using this program."
+-----------------------------------------------------------

Now it looks like we could get to the coins one by one: 

+-----------------------------------------------------------
| print "Welcome to the Vending Machine!"
| 
| line = raw_input("enter> ")
| 
| while line != "done":
|     coins = line.split()
|     for coin in coins:
|         print coin
|     line = raw_input("enter> ")
| 
| print "Thanks for using this program."
+-----------------------------------------------------------

If we can establish a balance and update it every time we look at a coin we're basically done: 

+-----------------------------------------------------------
| print "Welcome to the Vending Machine!"
| 
| line = raw_input("enter> ")
| 
| balance = 0
| 
| while line != "done":
|     coins = line.split()
|     for coin in coins:
|         if coin == "dime":
|             balance += 10
|         elif coin == "quarter":
|             balance += 25
|         elif coin == "nickel":
|             balance += 5
|         else:
|             print "I don't understand", coin
|         print "$" + str(balance / 100.0)
|     line = raw_input("enter> ")
| 
| print "Thanks for using this program."
+-----------------------------------------------------------

And that's basically it.