CSE115: Introduction to Computer Science I Dr. Carl Alphonce 219 Bell Hall 1

Announcements First class? Print a syllabus from web site. Turn in syllabus signature sheet if you haven’t already done so. Recitations begin this week. 2

cell phones off laptops away 3

Today Representing things –information encoding –symbol interpretation But first… 4

Put your name signs out! And the winner is: Taz 5

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

7 Spaces of different lengths is needed to decode unambiguously. Without spaces, how many ways can six dots in a row be decoded? (Image in public domain: ile:Intcode.png)

8 5 five cinq

Counting Decimal (base 10) etc. Binary (base 2) etc. 9

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

Same information Different encoding Color (RGB & CMYK) Quantity (Decimal & Binary) 11

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 12

Interpretation QUESTION: –What does 1101 represent? 13

Interpretation QUESTION: –What does the bit string 1101 represent? ANSWER: –Whatever we want it to represent! 14

Bit-string representations (used in computers) Binary (non-negative numbers) Two’s complement (integers) IEEE 754 (approx. floating point numbers) ASCII / EBCDIC / Unicode (characters) etc. 15

Questions? 16