1. CSE111: Great Ideas in Computer Science Dr. Carl Alphonce 219 Bell Hall Office hours: M-F 11:00-11:50 645-4739 alphonce@buffalo.edu

2. Announcements No recitations this week or next. First meeting of recitations in week of 1/25- 1/29. Extra copies of syllabus available at front of class 2

3. cell phones off (please) 3

4. Today Representing data Binary numbers 4

5. Images 5 Each pixel encodes the amount of RED, GREEN and BLUE (RGB). This is an additive color scheme. Printing uses CYAN, MAGENTA, YELLOW and BLACK (CMYK). This is a subtractive color scheme.

6. Morse Code Dots, dashes and spaces used to represent letters/digits http://www.planetofnoise.com/midi /morse2mid.phphttp://www.planetofnoise.com/midi /morse2mid.php Two features: –variable length encodings –not a prefix code 6

7. 7 Spaces of different lengths is needed to decode unambiguously. Without spaces, how many ways can six dots in a row be decoded?

8. 8 5 five cinq

9. Counting Decimal (base 10) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 etc. Binary (base 2) 0 1 10 11 100 101 110 111 1000 1001 1010 1011 1100 1101 etc. 9

10. Bit string A ‘0’ or ‘1’ is a binary digit, or a bit. A sequence of bits is called a bit string. For example: –1101 is a bit string 10

11. Number systems Decimal (base 10) Each position is weighted by a power of 10. E.g. 734 = –7*100 + 3*10 + 4*1 –7*10 2 + 3*10 1 + 4*10 0 E.g. 1101 = –1*1000 + 1*100 + 0*10 + 1*1 –1*10 3 + 1*10 2 + 0*10 1 + 1*10 0 Binary (base 2) Each position is weighted by a power of 2. E.g. 111 = –1*4 + 1*2 + 1*1 = “seven” –1*2 2 + 1*2 1 + 1*2 0 E.g. 1101 = –1*8 + 1*4 + 0*2 + 1*1 = “thirteen” –1*2 3 + 1*2 2 + 0*2 1 + 1*2 0 11