CSC151.01 2014F, Class 04: Computing with Symbols and Numbers

Overview

Preliminaries

Continue to work with the person you worked with yesterday (at the same computer).
Thursday at 10 am, I will hold a review session. It's an opportunity for you to ask anything you'd like about the class. You can also come in and work on labs or homework and have me around for questions.
There's a review session tonight at 8pm in CS Commons (3817)
There's a review session tomorrow night at 7:30 pm. (somewhere)
The review sessions will be a good place to learn more about, say, the modulo operation (which is likely to be on the quiz).
You have assigned partners for HW 2. I'll give you five minutes at the end of class to get together and set up a time/place to meet.

I'll take attendance again today since it's a way for me to learn names.
- Listen to the names so that you can identify your homework partner.

Lab writeup for today (due Friday): Execise 2, parts d, e, and f.
See link on schedule or list of labs for link to submit it.
HW 2 assigned. Due next Tuesday.
- Homework partners assigned. I'll give you five minutes at the end of class to find your partners.
Quiz Friday!
Reading for Friday:
- Drawings as Values

Note: Please send a short (one paragraph) reflection on any extra credit activity you attend. And reflect, don't summarize.

Awesome show at the Faculoner gallery.
CS Extras Thursday at 4:30 p.m. in Science 3821. Adam Arsenault on his internship at the Free Software Foundation. (The folks who are responsible for the GNU project.)
CS Table Friday: The Mythical Man-Month, Chapter 2.

In order to write an algorithm, you need to know what the computer (or other follower of instructions) can do
Different kinds of values suggest different basic operations
Both computer scientists and programming languages classify values ("type")
- Numbers - add, subtract, multiply
- Strings - concatenate, (speak aloud), get a letter or word, ...
We will regularly look at various types and consider the core operations we can use with that type
Today: Focus on two basic types (and variants)
- Numbers (whole, decimal numbers, complex numbers, fractions/rationals)
- Symbols - create and compare
We also care about representation

Why is 2.0 an integer?

Algortihm: How do you know if a number is an integer? "No fractional component" 5. 2.3

Relationship between mod and remainder

Same for positive numbers
For negative numbers, there are different ways to interpret remainder
Consider -11/4. Is that -3, with a remainder of 1, or is that -2 with a remainder of -3?
mod gives the first interpretation; remainder gives the second.
- mod policy Do inexact numbers always have a decimal point?
A decimal point signals to Scheme (or Scheme signals) that it's inexact.