CS50 Test #2						April 21, 1995
Open book and notes.  Answer all questions.

1.  (5 minutes) Consider the No Account stack (p 120).  Suppose we wanted to 
add a feature by that would display for the user the number of persons 
(accounts) that had more than 10 payments remaining and a balance greater than 
1000.  Describe, in general terms, how you would add that feature to this stack

2.  (10 minutes)  Develop a script that would accomplish the task described in 
question 1.

3.  (5 minutes) Describe briefly the binary, decimal, and ASCII representations
of information, including how each one is related to computers and programs.  

4.  (5 minutes) Below is an 8-bit binary number.  What decimal number does it 
represent?  What ASCII character does it represent?  (Show all work in this 
calculation.)

	01111000

5.  (10 minutes)  Below is an assembly language program.  Show all values that 
will appear in the accumulator while it is executing.

	[1]	LOD	6
	[2]	ADD  	7
	[3]	ADD  	8
	[4]	STO   	9
	[5]	HLT
	[6]	4
	[7]	2
	[8]	5
	[9]		

What would this look like if it were rewritten as a Hypercard script, assuming
that locations 6, 7, 8, and 9 were identified as the variables X, Y, Z, and 
ANS, respectively?

6.  (10 minutes)  A comparator is a circuit that determines whether two inputs 
are equal or not, and outputs 1 (true) or 0 (false) accordingly.  A one-bit 
comparator is shown in Figure 6.7 on page 226.  
a)  What are the outputs of all gates in this circuit when its inputs are P=1 
and Q=0?
b)  Describe in general how you would design a two-bit comparator -- that is, 
one that takes two 2-bit inputs (say P1P2 and Q1Q2) and outputs 1 or 0 
depending on whether or not both P1=Q1 and P2=Q2.  For instance, its output 
would be 1 for P1P2=01 and Q1Q2=01, but its output would be 0 for P1P2=01 and 
Q1Q2=10.

7.  (10 minutes)  Consider the scene on the back of this sheet.  Describe, in 
terms of basic Jabka objects (spheres, pyramids, etc.), how this particular 
scene might be modeled.  By writing directly on the back of this sheet, 
indicate what transformations would be needed to give each of these objects 
the right size and location in the scene.  As a point of reference, assume
that the pyramid in the scene is centered at the origin (0, 0, 0) and is in 
the middle of the table.  


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The scene shown on the back of the test sheet showed a table with four 
rectangular legs and a pyramid-shaped object sitting on its top.

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