CSC152 2005F, Class 18: Loops

Admin:
* Read "Separating What from How: Interfaces in Java" (and yes, it's ready)
* I've made significant changes to the next few weeks of the schedule.
* Thanks for the editing of the readings
* Attending football games; attending soccer games; attending x-country; basketball meets earns you extra credit
* Attending swing dances earns you extra credit (Nov. 4)
* Questions on the exam?
* Eryn will be available to answer general questions (e.g., on the Exceptions lab you did not complete) Tuesday from 7-8 p.m.

Overview
* Quick overview
* Lab

/Exam Questions/

* How do I test for end of file?  When your BufferedReader returns
  null (not the empty string), you've hit the end of file.
* What about blank lines?
  You get the empty string
* How do I write "the double quote character"?  "\""

/Loops/

Three kinds of loops in Java: While, For, Do

while (CONDITIONAL-EXPRESSION) 
{
  BODY
}
STUFF-AFTERWARD

"As long as CONDITIONAL-EXPRESSION is true, execute the body.":

x = 5;
while (x < 10) {
  x = x + 1;
  pen.println(x);
}

Prints 6, 7, 8, 9
Does it print 10?  Yes
IMPORTANT POINT: COND-EXP is only tested ONCE per execution of the body, not after every step

What do for loops look like?
Generally
for (INIT; TEST; INCREMENT) {
  BODY;
}
EQUIV TO
{
  INIT;
  while (TEST) {
    BODY;
    INCREMENT;
  }
}
Clearer when you write code

for (int i = 5; i < 10; i++) {
  pen.println(i);
}

Can you have multiple initial values and increments and such?
Yes, but it gets ugly

Can you explain i++
* It means "add one to i, changing the value of i"
What about ++i
* It means "add one to i, changing the value of i"
So how do they differ?
* If you use them in an expression, the value of ++i is the new value of i and the value of i++ is the old value of i
  i = 3;
  x = ++i;
  y = i++;
  // x has value 4 and y has value 4 and i has value 5

What does "while (!done)" mean
* done is a boolean variable.  It has values true or false
* ! means "not"
* Intent: Keep going until I explicitly note that I'm done
  * Note that I'm done by assigning true to done
	done = true;
* Terminology: done is a "loop sentinel"