CS100J, Fall 2001
Weds 9/13
Lecture 5
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Announcements:
+ new? See Overview on www.cs.cornell.edu/Courses/cs100j/2001fa/!
  see also Grading-->Adding Late
+ P1 leftovers goto Carpenter by Fri 5pm
+ P2 still due 9/18 -- late submission for holidays and recent events OK 
  (need to attach note and/or letter to front)
+ Next week: Chap 4.1, Chap 5.1-5.4 (9/25,9/27)
+ Next-Next week: All of Chap 4
+ group sessions!
+ MATLAB pol
+ New section: Maybe Weds?
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Topics:
+ more operators: mod (%)
+ more on assignments: named constants, final, swapping values
+ selection statements
+ loops (another kind of statement), using $while$
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More on operators:
+ remainder: %
   x % y generates the remainder of x/y
   ex) 10 % 5 -> 0  (10/5 = 2 with 0 as remainder)
       10 % 3 -> 1  (10/3 = 3 with 1 as remainder)
+ string equality
  use $.equals$ (why? Strings are technically objects!)
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More on assignments:
+ named constants
  - use variables for commonly used numbers
  - style: improves reuse and readability
  - but not truly constant because you could reassign
+ constants
  - can make variables "unvariable" with $final$:
    $final$ type variable = value 
  - final varibles known as CONSTANTS
  - won't be able to reassign a constant
  - style: usually write a constant as UPPERCASE
+ swapping variable values

  int tmp, x, y;
  x=1;y=2;

  tmp = y;
  y = x;
  x = y;
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Conditions:
+ execution of program goes in order of operators, starting from 1st statement
+ some say "top-down" execution
+ some statements can change FLOW OF CONTROL 
  (order of which statements execute)
+ sometimes need to make choices (example: comparison)
+ tree concept
+ use if, if-else (and if-else if)
+ syntax:

  if (c) // if c is true
    s;   // do s
         // otherwise, skip this statement

  if (c) // if c is true
    s1;  // do s1
  else   // otherwise
    s;   // do s2

+ other varieties:

  if (c1)
    s1
  else if (c2)
    s2

  if (c1)
    s1;
  else if (c2)
    s2;
  else
    s3;

+ can have as many else-ifs as you wish
+ indent statements, but entire body counts as SINGLE statement!
  (indenting does not make a new statement, just improves clarity)
+ can do multiple statements under each condition:
  - use statement block
  - { statements }
+ 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
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More on conditions:
+ nested selection statements
+ each selection statement is indeed a statements
+ 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");
+ sometimes you can compress nested ifs with logical operators
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Loops:
+ what if need to repeat something?
+ could use lots of assignments and conditions, but....
+ avoid redundancy to clarify code 
  (spaghetti code)
+ repetition? use loops (repetition statements)
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Syntax:
+ $while$, $for$, $do$
+ focus on $while$
+ while(cond)
    s;
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Occasions to use:
+ definite
  - repeat/echo
  - accumulate
+ indefinite
  - conditional update
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