Section for Week 7, Tuesday, 2/23/99

1. Quiz on thursday -- base conversions.

2. Binary, hex, decimal
{binary,hex,octal} --> decimal: add up columns according to power of base
decimal --> other: figure out how many of each power fit in the number

Decimal	    hex	   binary
0	    0	   0
1	    1	   1
2	    2	   10
3	    3	   11
4	    4	   100
5	    5	   101
6	    6	   110
7	    7	   111
8	    8	   1000
9	    9	   1001
10	    A	   1010  (8+2)
11	    B	   1011
12	    C	   1100
13	    D	   1101
14	    E	   1110
15	    F	   1111
16	    10	   10000
134	    86	   10000110  (8 and 6 in hex)
243	    F3	   11110011
168	    A8	   10101000

So to go from hex to decimal and back, take 4-bit blocks.  Octal is same,
using 3 bit blocks (3 bits -> 2^3=8=octal, 4 bits->2^4=16=hexadecimal).

3. hidden fields in the state-preservation game (virtual vs. real forms)

4. LA#6 --> remember to change +'s to spaces (before or after hex conversion?)
	 go over various elements of the assignment--the Perl aspects and
	 the relationships between scripts, HTML, server, and client.

	 breakdown of LA#6:
	 1) Copy sub from P.  Make sure it works for you, and that you
	 understand everything it does.
	 2) Review O.  Write the sub in cgi_helper, and copy the testing
	 program from the handout.  Make sure this works.
	 3) modify Get_Form_data from 2) to make it handle multiple
	 selections, and modify the testing program to see it works
	 4) Modify form from prev. assignment to use a new CGI you write --
	 response.cgi which will check that certain obligatory fields exist,
	 and complain if they don't, allowing the user to re-enter them
	 (saving the values entered in other fields to minimize annoyance).

	 Submission: you'll be submitting cgi_helper (for parts 2&3), and
	 then the form and CGI from the last part (4).  No need to submit
	 the testing programs.