CS100J, Fall 2001
Tues 9/4
Lecture 2
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Announcements:
+ new? See Overview on www.cs.cornell.edu/Courses/cs100j/2001fa/!
+ Project 1 (P1) due Thurs 9/6
+ Staff page on website being updated this week
+ CW and Savitch in bookstore
+ reading for Thurs: Savitch Chaps 2.1-2.4, skip 82-85
+ future reading for Tues: 3.1, 3.4
+ consulting in lab: Labs-->Carpenter
+ office hours -- see Staff-->Staff Listing
+ revised sections: 
  - Section 17 (HO 314) goto Upson 111 (TA schedule conflict)
  - we will create new section at other time to compensate
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Topics:
+ reminders from previous lecture
+ reintroduction of DIS
+ CS100J policy reminders
+ lecture policies
+ objectives/advice
+ fundamental programming concepts
  - definition of programming
  - how programming works
  - problem solving
  - algorithms
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Reminders
+ CS99/CS100J/CS100M, alternatives
+ policies -- see website, click on everything, see Overview
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DIS
+ history, background
+ why CS100/intro courses?
+ pet peeves (reading newspapers, very late, walking in front during lecture, 
  arguing/pleading for late submissions)
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Problem solving
+ problems are physical and abstract
+ build models which are physical and abstract
+ models will solve the problem where we cannot/will not
+ use a computer! need to write software...
+ PROGRAMMING: automating problem solving
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Computer Rudiments
+ hardware:     physical components of a computer
+ software:     "the intelligence" that runs the hardware
                 - create with programming (coming up!)
+ information:  bits and bytes -- sequences of 1s and 0s (digits) that 
                represent non-digital information
+ memory:       "space" inside a computer to store information
                - software can "borrow" a portion to use
                - programming involves using memory
+ file:         collection of information with a name
+ directory:    collection of files
+ folder:       same as directory
+ path:         location of file or directory starting from the 
                 "uppermost" directory
+ ASCII/text:   characters found on the keyboard 
                - uses 8 bits to represent a character which is a byte
                - ASCII (or text) format is universal
                - can load into almost editor and wordprocessor
                - can edit files with programs called text editors
+ Program:      file composed of instructions using a computer language
                - usually text because we need to type those instructions!
                - the process of telling the computer to activate commands
                  in a program is called running or executing
                - information is passed from your text to the computer
                - computer activates each instruction in sequence
+ Interpreting: computer reads each line of code and acts up it before
                acting upon the next line
+ Compiling:    process of converting code into an unreadable format
                - more bits and bytes, but condensed
                - can create "runnable" (executable) files that quickly
                  run your programs
+ Input:        - any information you supply to a program
+ Output:       - any information reported by a program
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Process of Programming
+ start with problem
+ look for solution
+ brainstorm, outline, write, rewrite, polish
  (1) Gather data
      - figure out abstract and concrete "things" in problem
  (2) Gather processes
      - determine behaviors these "things" have
  (3) Algorithm
      - try to connect things and behaviors in a sequence of
        steps/instructions called an ALGORITHM
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Forming an algorithm
+ break solution down into sequence of steps
  (each step is an instruction)
+ use PSEUDOCODE (langauge that resembles a computer language)
  terms: repeat, if, else, otherwise, continue, return, stop, start, etc
+ avoid minutia and over-generality -- look for the middle...
  (often depends on task at hand!)
+ may have to keep breaking down steps
+ final algorithm is a program in "words"
+ example: think recipe
  - someone else wrote a sequence of instructions
  - used terms that are accepted and have known values/meanings
  - you, the human, act on the instructions
  - something is created and hopefully tastes good
+ general examples: scheduling of office hours, simulation of dishroom, 
  number guessing, etc
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Computer Language
+ need to translate English language algorithm into a computer language
+ many options: MATLAB, Maple, Java, C, C++, C#, etc
+ Choose MATLAB and Java for CS100
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Language Elements
+ computer language usually written (in the future, spoken)
+ has syntax (grammar) and semantics (meaning)
+ characters (keyboard symbols) -> tokens (words) -> statements (sentences)
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Characters
+ usually keyboard characters (ASCII text)
+ ASCII has 128 characters 
+ some are nonprinting -- see ascii.txt for full list
+ also, try entering $char(0:127)$ in MATLAB (do not enter $s: I use
  the $ notation to indicate a code fragment or statement to enter) 
+ technically, Java uses UNICODE
  - over 65000 characters
  - see p88, Appendix 3, website: Material->Java->Miscellaneous->UNICODE
  - special non-printing characters can be reproduced with ESCAPE CHARACTERS
    o see pp86-88
    o ex) \n (newline)
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Tokens
+ characters form "words", which are called TOKENS
+ tokens include:
  numbers, operators, variables, keywords, punctuation, 
  token separators, strings, comments (described in more detail soon)
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Statements
+ combine tokens to create "sentences", which are called STATEMENTS
+ each "sentence" forms an instruction/command
+ "sentences" are called statements
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Example of first program:

// FirstProgram
// DIS, 2001
// Program prints welcome message to the world.

public class FirstProgram {
   public static void main(String[] args) {
       System.out.println("Hello, world!");
   }
}