CPSC 100, Fall 1997:
Answers to Quiz #7

This is the seventh (and last) quiz from the course Computer Science 100: Principles of Computer Science, taught by David Eck. The answers that are included here are sample answers only. There might be many other answers to a given problem that would also receive full credit. See the home page for the text, The Most Complex Machine, for more information about the course.

Question 1: According to the video, Giant Brains, what was the original meaning of the term "computer"?

Answer: A person who computes. (Generally, a person who was employed to do long, tedious computations by hand.)

Question 2: According to the video, Giant Brains, why did Charles Babbage originally set out to build a computing machine?

Answer: He was tired of finding so many errors in tables produced by human computers, and wanted a machine that could compute such tables automatically and without errors.

Question 3: According to the video, Giant Brains, what was one of the roles that women played in the history of computing?

Answer: There are several possible answers. The first programmer, Ada Lovelace, was a woman who worked with Charles Babbage. Most of the women computers who worked on firing tables during World War II were women. Women did the actual programming of the ENIAC by setting switches and rewiring connections.

Question 4: According to the video, Giant Brains, when the ENIAC computer was fitted with special blinking lights for a publicity film, what were those lights made from?

Answer: Ping-pong balls.

Question 5: According to the video, Giant Brains, what was Alan Turing's key insight about the nature of computing? How did his view differ from that of most of his contemporaries?

Answer: Turing realized that computers could do more than numerical calculations. He saw that computers could work with arbitrary symbols, and therefore could be employed to work on a limitless number of different tasks -- up to and including the simulation of intelligence. His contemporaries saw computers as fast automatic calculators, and therefore missed seeing their truly revolutionary potential.

Question 6: What is the basic difference between painting and drawing programs?

Answer: In a painting program, the user creates an image by coloring pixels. The only data that the computer remembers is the color of each pixel. The computer does not know about objects in the scene, and therefore it is not possible for the user to manipulate those objects as such. In a drawing program, the computer keeps a database containing information about all the objects in the scene. The computer "renders" the scene described by this database. The objects can be manipulated by, for example, moving them, rotating them, resizing them, or changing their color.

Question 7: Define the term rendering, as it applies to computer graphics.

Answer: Rendering refers to the process of taking a scene description (or "model") and computing a visual representation of that scene. The scene description is a database with information about the objects in the scene such as their color, size, position, surface texture, and so on. The computer has to take this information and decide how to display an image of the scene by setting the colors of individual pixels.

Question 8: Describe the animation produced by the following xModels scene description:

            animate 30
            square  scale 5:1  translate 0:-5 0
            square  scale 5:1  translate 0:5 0

Answer: This is an animation consisting of 31 frames. Two squares start at the center of the scene. One square moves to the left as the animation progresses. The other moves to the right. As the squares move, they shrink in size from an initial size of 5 units down to a final size of one unit.

David Eck, 13 November 1997