Welcome to 4020!

Useful Tip You can populate your Google Calendar with your classes using Flyboy's .ics File Generator. This is what I did.

This is YOU

This section will place a greater emphasis on JavaScript than in the past. YOu will be a guinea pig for this experiment. Yeah, that has its perils, but it can also have big advantages. So, this will be a learning experience for all of us!

Making Pods

This will be done with a randomization procedure. Get to know your podmates. There is safety in numbers. If you miss class, they can debrief you.

A Homily on Your Lappy

The Book

Numbers

What is number? Download numbers.pdf from canvas. We will have a quiz on this reading.

These are not numbers, they are representations of the same number.

256     (decimal/base 10)
CCLVI   (roman numerals)
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

If we have collections A and B, we can pair items off until one collection is exahusted.

if A has a leftover:
    A is bigger
if B has a leftover:
    B is bigger
if no leftovers
    A and B have the same size.
    A and B have the same number of elements.

This abstract notion of "samesizeness" is the actual notion of number.

A desirable quality of a system of number representation is compactness.

Also, how easy is it to do (integer) arithmetic?

• + addition
• - subtraction
• * multiplication
• // integer division
• % mod

To compute b % a you divide a into b and find the remainder.

365%7 = 1

What day of the week is it 1000 days from now?

1000 % 7 = 6.

Today is Tues, so if we count 6 days ahead (or one back), it's a Monday.

The rules for leap year can be expressed using mod.

Very four years the year leaps, so the year leaps if year % 4 == 0

BUT there si an exception very 100 years, (if year % 100 == 0)

BUT every 400 years, there is an exception to the exception! this occurs if year % 400 == 0.

Tally Arithmetic

addition concatentate (glue together)

subtraction Suppose we want to compute

IIIIII - IIII

    IIIIII
      IIII  (cancel away the smaller ones)
    ------
    II

Multipwy For each of the first factor, make a copy of the second.

   III * IIII

   IIII
   IIII
   IIII

Now glue 'em.

Divide Suppose we want to compute IIIIII / IIII.

We just count how many times you can chop right out of left.

    I      II / IIII   One chop did it.
    IIIIII // IIII = I.

Mod We get this for free. It's the leftovers from division.

  IIIIII % IIII  = II

Lack of compactness is the downfall of tally marks. Arithmetic is butt simple, but look at NCSSM's enrollment.

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII