CS 100, Summer 2001
Thursday, 6/28
Lecture 4 
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+ Collect Assignment 1
Announcements: 
+ Pick up (graded) Exercise 2
+ Exercise 3 due Friday
+ reading: Savitch 2.2 (Strings) and 3.1 (Cond operator)
+ Ben and Hongie's office location (328)
+ Assignment 2 will be handed out on Monday (7/2), not Friday 
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Topics: 
+ more operators
+ conditional statements
+ while loops
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Misc:
+ taking notes: don't need to write all the code down (see webpage)
+ do write down what goes on the board
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Review/summary from last time
+ operators (arithmetic, comparison, boolean)
+ expressions
+ statements (empty, block, assignment)
+ conditional statements (if, switch)
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+ Operators: 
  + type casting. (see Lecture4.java)
  - ex) mixing doubles and ints makes doubles
        System.out.println(1.0/2) yields 0.5
  - use CAST to force different value
  - syntax: (type) expression
  - ex) System.out.println( (int) 9.8) yields 9 (an integer)
  - You also saw this in Exercise 1
  + operators: ++, --, +=, etc.
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Statements: 
+ Assignment:
  - changes the program's STATE
+ Java executes each statement top-down, left-to-right
  (within a statement, operator precedence determines direction of execution)
+ some statements can change FLOW OF CONTROL 
  (order of which statements execute)
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Conditions:
+ Motivation: 1) make choices, 2) sanity checks
+ language elements:
  - if, else are keywords
  - conditions? must evaluate to true or false (Boolean)
    o relations: <  (less than)           > (greater than)
                 <= (less than or equal)  > (greater than or equal)
                 == (equal, but do NOT use =)
                 != (not equal)
    o logic:     && (and)  || (or)  ! (not)
    o values:    true  false
  - example: see Lecture4.java
+ nested selection statements
+ each selection statement is indeed a statement
+ so, the statements in the selection statements could be another selection!
+ ex) 
  if (temperature < 100)
     if (temperature > 80)
        System.out.println("hot");
     else
        System.out.println("not hot");
+ else AMBIGUITY (dangling else: which 'if' does the 'else' go to?)
+ Java default: 'else' attaches to nearest 'if'
+ indentation doesn't solve this
+ hence our rule: ALWAYS use curly braces! 
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Loops:
+ statement for repeated actions
   - repeat calculation
   - accumulate values (statistics)
   - clues that you should use a loop: "do something to every..", "do
   something until..." 
+ powerful addition to your Java repertoire!
+ loops are known as REPETITION statements
+ while (b) 
  { 
    s;
  }
  - b must be boolean
  - s might be any statement
EXAMPLE: Div3.java, WhileLoop.java
+ loop design: 
  - setup (gather data, assign variables)
  - condition (check for when to stop)
  - processing (do tasks, update)
  - postprocessing (account for what may have happened; output)
+ more examples next time!
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PICK UP Exercise 3 (handout), Exercise 2 (graded)