CS100J, Spring 2001
Tues 2/5
Lecture 5
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Announcements:
+ P2 due Thurs 2/8 (include E2 even if you did it!)
+ T1 (prelim 1) Tues 2/13
+ AEWs for CS100J: some sopts open (see Announcements)
+ new section: Tues (today) 12:20-1:10 Philips 407
+ 3.3 in Savitch: use $while$
+ give lecture notes and online examples "speech"
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Topics:
+ notation: $...$, boldface-courier
+ operators: cast, %, ++, --, +=
+ loops: $while$, patterns, types
+ methods: $Math.random$, $Math.floor$, $Math.pow$ (see pp316-318)
+ scope diagrams? (might have to hold off on this)
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Summary from Lecture 4:
+ loops: repeat actions
+ known as REPETITION statements
+ $while(c)$ s;
- c must be boolean
- s might be any statement
+ BLOCK (COMPOUND) statement {s1; s2; ..., sn;}
- all statements grouped together
- typical use for condition and selection statements
+ loop design:
- preprocessing (gather, assign data)
- processing (enter loop by testing condition, do tasks)
- postprocessing (account for what may have happened)
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Important Examples:
+ See Spring 2000 examples for additional help
+ everything up to nested2
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I/O:
+ in labs, CUCS (TokenReader) already installed
+ just include statement:
TokenReader in = new TokenReader(System.in);
+ that line will show up on exams
+ for those w/o TR, put TR or equivalent in Project (.java in Sources, .class
in Classes)
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More on operators:
+ the followings operators show up in loops often
+ remainder: % (pp70-71)
- 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)
+ increment: ++, --, += (pp77-79)
- used for shortcuts
ex) $count = count + 1$
replaced with
$count++$ or $++count$
- works also with -- to decrease by 1
- are ++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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More on assignments:
+ swapping variable values
+ shows up in loops often
int tmp, x, y;
x=1;y=2;
tmp = y;
y = x;
x = y;
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2 generalizations of loops:
1) definite
- repeat/echo (could use $for$ -- discussed later)
- accumulate
indefinite
- conditional update
2) patterns
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Style:
+ indentation (under $while$)
+ avoid $break$, $System.exit$ (pp 175-177)
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