Christopher Verdery's Java Webpage

     Sometime during the year, I must make a webpage.  As much fun as it sounds, I've yet to make it, so I'm forced to do it now.  My topic will be...

    It computer programming the need for looping arose.  Programmers wanted an action to repeated until a certain condition was satisfied.  So they were given while statements.  But it wasn't enough.  They soon found themselves typing a similar pattern:
 

    Programmers soon tired of this repeated structure which wasn't mean to repeat under a condition , it was meant to repeat a certain number of times.  So the for statement was born.  It's basic structure is:
 
 

where variable1 is a local, numeric value (usually an int, but not necessarily), start is your initial value, and end is your last value, but not exactly.  Because the loop may never reach exactly the end value, it is stated as a conditional statements similar to those found in while statements.  In between variable1 and end is rationalOperator, which can be any rational operator, but is usually either <= or =>, based on variableIncrement, which tells how to edit, or update, variable1.  Common uses of this are i++ for positively incrementing values, and i-- for countdowns.  The actions of the for statement are included in block statement.

Note: variable1 is local, meaning that unless it's been predefined in the program, you must intialize it.  After the loop runs, it will lose its redefined value and if instatiated, be deleted.  This is so excess values will not be stored.  

    There are many uses of a for statement.  For instance, to calculate interest on a bank account, one must use for statements to continuously calculate money, if do not want to use the insanely handy P(1+r/100)^t*r/n, we can use for statements to do this.
For example:  
 

Ain't she wonderful, folks?  Now, we can calculate the amount of money in our banking account after a set number of years (n), assuming the bank updates annually, instead of quarterly, monthly, weekly, daily, hourly, minutely, secondly, or continuously. But we can edit the code to do that!  That'll be your first exercise.  Create a program using this as a shell for part of the program.  It will have parameters, hopefully.  Probably if-else statements.  Look them up.  I don't have time to tell you about them.

For more on for statements, see any of the following:

Susan Anderson-Freed

Diagrams

Elliott e Rusty Harold's Brewing Java: A Tutorial

This is the most inopportune time to mention the book we are using, but I guess here's better than anywhere.  It's called Computing Concepts with Java Essentials by Cay Horstmann.

   
Now that we know all about for statements, let's talk about mistakes that stupid programmers such as yourselves make.  The first one is reading a webpage from a novice, cynical, self-righteous student in a unually lazy programming class.  What you messed up already?

Mistake #1: Inconsistancy of condition and update

For example:

    See the problem?  Me neither.
    Oh, you do?  Okay, me too.  The program will increment forever!  Now, there are probably better examples of how a programmer would mess up than this, but you get the idea, right?  Here's a vocabulary term: range.  It's the set of numbers that one would like to increment while one is talking in the indefinite person tense.  Let's say you wanted to find the square of all the numbers from 0 to 10.  If you don't know them by heart, go back to fourth grade, please.

    Before we, start let's establish some things.  First, what variable do we want to use?  Well, these values are all integers, so it's a safe bet we can use an int.  We want to start with 0, so that's our initiation value.  We want to stop at 10 (mind the italics), so we want the value to increment until it equals (you're minding the italics, aren't you?) 10, so it's less than or equal to 10 (>= 10), and finally, we want every number from one to ten, so we can use the ++ shorthand.

Mistake #2 (of 2; this page is rather short): Using the Forbidden Operator  

For example

Now, just for you, I've created number that will work out... maybe.  The forbidden operator is the not-equal-to operator (!=). Because of scary limited precision, using this may create a rounding error, so the variable, in my case ickyDecimal, will never quite equal 31.4205, even though to the common laymen (with a calculator, because the common laymen can't do math anymore), if you continue to add 1.04783 to 3.12904 repeated, you will eventually come up with 31.4205.  Don't yell at the computer.  It can't hear you.  Unless it has an audio input device, then it can hear, but it won't care, because it is (1) an inanimate machine and (2) likely possessed by a meticulously peevish demon, or in Karen Lockhart's case, Satan.  Just use the less-than (<) or the less-than-or-equal-to operator (<=), and you will in most cases be fine.  I promise.  Just don't yell at me if you're not.   I can't here you either.

Well, if you have any questions, I am an amateur programmer who will be of little use to you, so please e-mail on an e-mail account that I cannot access outside of school, especially during the summer, which will destroyed sometime around June 2004, on a network that crashes often.  And this website?  Maybe it will never disappear.  It depends on my teacher.  Please visit his webpage with the link at the top of the page.  Don't worry, we're pretty confused by it, too, sometimes.

But if you think you may have gotten for statements down cold, feel free to use these Exercises from jGuru at Java Sun.

E-mail me: Christopher Verdery

The Writings of Lord Godeerc VanDrey (Note: This is not a link to a for statements-related page. You have been warned.)
 

©2003 Creedog, Inc.  A Division of Godeerc VanDrey Enterprises, Inc.  This page was last updated Monday, May 5, 2003.  You'll be lucky if it is ever updated again.