CS100J, Fall 2001
Tues 9/28
Lecture 6
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Announcements:
+ Mike Scovetta filling in today
+ AEW reps visiting
+ new? responsible for www.cs.cornell.edu/Courses/cs100j/2001fa/
  start with Overview and Grading-->Adding
+ reading Next week: Chap 4.1, Chap 5.1-5.4 (9/25,9/27)
+ Next-Next week: All of Chap 4
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Topics:
+ selection statements
+ $while$
+ categories of loops
+ increment operators
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Repetion statements/loops:
+ what if you need to repeat something?
  - you could use lots of assignments and conditions
  - you want to avoid redundancy to clarify code
+ use REPETITION STATEMENTS to repeat actions
+ introducing new keyword: $while$
+ syntax for $while$:

  while(c)
      s;

  c: boolean expression
  s: might be any statement or block statement

  reminder: block statement {s1; s2; ..., sn;}
  - all statements grouped together
  - typical use for condition and selection statements
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example: toy probs
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Other keywords:
+ $for$
+ $do$
+ not allowing these for awhile (forgive the pun)
+ why? $while$ is "most pure"
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Style:
+ indentation (under $while$)
+ avoid $break$, $System.exit$ (pp 175-177)
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Increment operators: ++, --, +=, *= (pp77-79)
+ used for shortcuts  
  ex) $count = count + 1$
      replaced with 
      $count++$ or $++count$

+ works also with -- to decrease by 1
+ Question: ++var and var++ identical? NO
  ex) int a,b,c,d;
      c = 1; d=1;
      a = ++c; // a gets c<-c+1: so, c gets 2, and then a gets 2
      b = d++; // b gets c and then c<-c+1: so, b gets 1 and then d gets 2

+ others: $count = count + 7$;
          $count += 7$;
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Loop design:
+ preprocessing (gather, assign data)
+ processing (enter loop by testing condition, do tasks)
+ postprocessing (account for what may have happened)
+ 2 generalizations of loops:
  (1) definite
      - repeat/echo (could use $for$ -- discussed later)
      - accumulate
  (2) indefinite
      - conditional update
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