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  • Raising C# events with an extension method - is it bad?

    - by Kyralessa
    We're all familiar with the horror that is C# event declaration. To ensure thread-safety, the standard is to write something like this: public event EventHandler SomethingHappened; protected virtual void OnSomethingHappened(EventArgs e) { var handler = SomethingHappened; if (handler != null) handler(this, e); } Recently in some other question on this board (which I can't find now), someone pointed out that extension methods could be used nicely in this scenario. Here's one way to do it: static public class EventExtensions { static public void RaiseEvent(this EventHandler @event, object sender, EventArgs e) { var handler = @event; if (handler != null) handler(sender, e); } static public void RaiseEvent<T>(this EventHandler<T> @event, object sender, T e) where T : EventArgs { var handler = @event; if (handler != null) handler(sender, e); } } With these extension methods in place, all you need to declare and raise an event is something like this: public event EventHandler SomethingHappened; void SomeMethod() { this.SomethingHappened.RaiseEvent(this, EventArgs.Empty); } My question: Is this a good idea? Are we missing anything by not having the standard On method? (One thing I notice is that it doesn't work with events that have explicit add/remove code.)

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  • Most awkward/misleading method in Java Base API ?

    - by JG
    I was recently trying to convert a string literal into a boolean, when the method "boolean Boolean.getBoolean(String name)" popped out of the auto-complete window. There was also another method ("boolean Boolean.parseBoolean(String s)") appearing right after, which lead me to search to find out what were the differences between these two, as they both seemed to do the same. It turns out that what Boolean.getBoolean(String name) really does is to check if there exists a System property (!) of the given name and if its value is true. I think this is very misleading, as I'm definitely not expecting that a method of Boolean is actually making a call to System.getProperty, and just by looking at the method signature, it sure looks (at least to me) like it should be used to parse a String as a boolean. Sure, the javadoc states it clearly, but I still think the method has a misleading name and is not in the right place. Other primitive type wrappers, such as Integer also have a similar method. Also, it doesn't seem to be a very useful method to belong in the base API, as I think it's not very common to have something like -Darg=true. Maybe it's a good question for a Java position interview: "What is the output of Boolean.getBoolean("true")?". I believe a more appropriate place for those methods would be in the System class, e.g., getPropertyAsBoolean; but again, I still think it's unnecessary to have these methods in the base API. It'd make sense to have these in something like the Properties class, where it's very common to do this kind of type conversions. What do you think of all this ? Also, if there's another "awkward" method that you're aware of, please post it. N.B. I know I can use Boolean.valueOf or Boolean.parseBoolean to convert a string literal into a boolean, but I'm just looking to discuss the API design.

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  • C#: An object reference is required for the non-static field, method, or Property

    - by Omin
    I feel bad for asking this when there are so many questions that are related but I was not able to find/understand the answer I am looking for. // 2. Develop a program to convert currency X to currency Y and visa versa. using System; class Problem2 { static void Main (string[] args) { while (true) { Console.WriteLine ("1. Currency Conversion from CAD to Won"); Console.WriteLine ("2. Currency Conversion from Won to Cad"); Console.Write ("Choose from the Following: (1 or 2)? "); int option = int.Parse( Console.ReadLine() ); //double x; if (option == 1) { Console.WriteLine ("Type in the amount you would like to Convert CAD to Won: "); //double y =double.Parse( Console.ReadLine()); //Console.WriteLine( cadToWon( y ) ); Console.WriteLine( cadToWon( double.Parse( Console.ReadLine() ) )); } if (option == 2) { Console.WriteLine ("Type in the amount you would like to Convert Won to CAD: "); Console.WriteLine( wonToCad (double.Parse( Console.ReadLine()))); } } } double cadToWon( double x ) { return x * 1113.26; } double wonToCad( double x) { return x / 1113.26; } } This give me the Error messgae "An object reference is required for the non-static field, method, or property 'Problem2..." I know that I'll be able to run the program if I add static infront of the methods but I'm wondering why I need it (I think it's because Main is static?) and what do I need to change in order to use these methods without adding static to them? Thank you

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  • C# Method not returning a unique value when it should be.

    - by Josh King
    I have two methods, generateNounPhrase() and generateVerbPhrase(). VerbPhrase will call on NounPhrase half the time and it's output the output should be something to the effect of: the empty lot re-animates this pyramid (bold indicating where generateNounPhrase() is logically called). The true output however is in the form of: the empty lot re-animates the empty lot At first I thought my randomIndex method wasn't working as I had intended, but if I run the two methods again I do get different noun phrases but they are not unique at the beginning and end of the sentence as they should be. Any idea what I am doing wrong in order to get one method to show the same result? private string generateNounPhrase() { string nounPhraseString = ""; nounPhraseString = nounMarkersStringList[randomIndex(0,nounMarkersStringList.Count-1)]; if (included(1, 4, 2) == true) { nounPhraseString += " " + adjectivesStringList[randomIndex(0, adjectivesStringList.Count - 1)]; } nounPhraseString += " " + nounsStringList[randomIndex(0, nounsStringList.Count - 1)]; return nounPhraseString; } private string generateVerbPhrase() { string verbPhraseString = ""; if (included(1, 4, 2) == true) { verbPhraseString = intransitiveVerbsStringList[randomIndex(0, intransitiveVerbsStringList.Count - 1)]; } else { verbPhraseString = transitiveVerbsStringList[randomIndex(0, transitiveVerbsStringList.Count - 1)] + " " + generateNounPhrase(); } return verbPhraseString; }

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  • Finding an odd perfect number

    - by Coin Bird
    I wrote these two methods to determine if a number is perfect. My prof wants me to combine them to find out if there is an odd perfect number. I know there isn't one(that is known), but I need to actually write the code to prove that. The issue is with my main method. I tested the two test methods. I tried debugging and it gets stuck on the number 5, though I can't figure out why. Here is my code: public class Lab6 { public static void main (String[]args) { int testNum = 3; while (testNum != sum_of_divisors(testNum) && testNum%2 != 0) testNum++; } public static int sum_of_divisors(int numDiv) { int count = 1; int totalDivisors = 0; while (count < numDiv) if (numDiv%count == 0) { totalDivisors = totalDivisors + count; count++; } else count++; return totalDivisors; } public static boolean is_perfect(int numPerfect) { int count = 1; int totalPerfect = 0; while (totalPerfect < numPerfect) { totalPerfect = totalPerfect + count; count++; } if (numPerfect == totalPerfect) return true; else return false; } }

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  • Rails: (Devise) Two different methods for new users?

    - by neezer
    I have a Rails 3 app with authentication setup using Devise with the registerable module enabled. I want to have new users who sign up using our outside register form to use the full Devise registerable module, which is happening now. However, I also want the admin user to be able to create new users directly, bypassing (I think) Devise's registerable module. With registerable disabled, my standard UsersController works as I want it to for the admin user, just like any other Rail scaffold. However, now new users can't register on their own. With registerable enabled, my standard UsersController is never called for the new user action (calling Devise::RegistrationsController instead), and my CRUD actions don't seem to work at all (I get dumped back onto my root page with no new user created and no flash message). Here's the log from the request: Started POST "/users" for 127.0.0.1 at 2010-12-20 11:49:31 -0500 Processing by Devise::RegistrationsController#create as HTML Parameters: {"utf8"=>"?", "authenticity_token"=>"18697r4syNNWHfMTkDCwcDYphjos+68rPFsaYKVjo8Y=", "user"=>{"email"=>"[email protected]", "password"=>"[FILTERED]", "password_confirmation"=>"[FILTERED]", "role"=>"manager"}, "commit"=>"Create User"} SQL (0.9ms) ... User Load (0.6ms) SELECT "users".* FROM "users" WHERE ("users"."id" = 2) LIMIT 1 SQL (0.9ms) ... Redirected to http://test-app.local/ Completed 302 Found in 192ms ... but I am able to register new users through the outside form. How can I get both of these methods to work together, such that my admin user can manually create new users and guest users can register on their own? I have my Users controller setup for standard CRUD: class UsersController < ApplicationController load_and_authorize_resource def index @users = User.where("id NOT IN (?)", current_user.id) # don't display the current user in the users list; go to account management to edit current user details end def new @user = User.new end def create @user = User.new(params[:user]) if @user.save flash[:notice] = "#{ @user.email } created." redirect_to users_path else render :action => 'new' end end def edit end def update params[:user].delete(:password) if params[:user][:password].blank? params[:user].delete(:password_confirmation) if params[:user][:password].blank? and params[:user][:password_confirmation].blank? if @user.update_attributes(params[:user]) flash[:notice] = "Successfully updated User." redirect_to users_path else render :action => 'edit' end end def delete end def destroy redirect_to users_path and return if params[:cancel] if @user.destroy flash[:notice] = "#{ @user.email } deleted." redirect_to users_path end end end And my routes setup as follows: TestApp::Application.routes.draw do devise_for :users devise_scope :user do get "/login", :to => "devise/sessions#new", :as => :new_user_session get "/logout", :to => "devise/sessions#destroy", :as => :destroy_user_session end resources :users do get :delete, :on => :member end authenticate :user do root :to => "application#index" end root :to => "devise/session#new" end

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  • Cannot install packages. "Warning: untrusted versions..." plus "method driver /usr/lib/apt/methods/http could not be found"

    - by Steve Tjoa
    Judging from Internet forums, these errors appear to be popular when attempting to install packages: steve:~$ sudo aptitude install examplepackage The following NEW packages will be installed: examplepackage examplepackage-common{a} 0 packages upgraded, 2 newly installed, 0 to remove and 0 not upgraded. Need to get 1,834 kB of archives. After unpacking 7,631 kB will be used. Do you want to continue? [Y/n/?] WARNING: untrusted versions of the following packages will be installed! Untrusted packages could compromise your system's security. You should only proceed with the installation if you are certain that this is what you want to do. examplepackage examplepackage-common Do you want to ignore this warning and proceed anyway? To continue, enter "Yes"; to abort, enter "No": Yes E: The method driver /usr/lib/apt/methods/http could not be found. E: The method driver /usr/lib/apt/methods/http could not be found. E: Internal error: couldn't generate list of packages to download I followed this post by uninstalling ubuntu-keyring. But I cannot reinstall ubuntu-keyring or ubuntu-minimal -- the above errors reappear. In fact, I don't even seem to have apt (I must have caused this along the way by trying a bad solution, or maybe a clean): steve:~$ sudo apt-get update sudo: apt-get: command not found Aptitude works, but I can't install apt: steve:~$ sudo aptitude install apt The following NEW packages will be installed: apt 0 packages upgraded, 1 newly installed, 0 to remove and 0 not upgraded. Need to get 1,046 kB of archives. After unpacking 3,441 kB will be used. E: The method driver /usr/lib/apt/methods/http could not be found. E: The method driver /usr/lib/apt/methods/http could not be found. E: Internal error: couldn't generate list of packages to download ...or update steve:~$ sudo aptitude update E: The method driver /usr/lib/apt/methods/http could not be found. E: The method driver /usr/lib/apt/methods/http could not be found. E: The method driver /usr/lib/apt/methods/http could not be found. I tried this post. Didn't help. To summarize, the main problem is that I cannot install anything. While attempting to fix the problem, the other aforementioned errors occurred. Can you help me fix this error? Feel free to ask if you need more information. Stats: steve:~$ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 11.10 Release: 11.10 Codename: oneiric

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  • Should I continue teaching old Java input methods alongside the new ones?

    - by user1598390
    I've been imparting a Java introduction course for several years. Some slides explain how to read from files and keyboard using BufferedReaders, InputStreams, FileInputStreamReaders etc. I'm adding slides explaining how to achieve this using more up to date approaches like Scanner. Should I leave out the old BufferedReaders, InputStreams and FileInputStreamReaders slides altogether, and teach only the new methods, or should I continue to teach these methods for the sake of completeness ? Will my students benefit from learning how to read from files and keyboard the old way ?

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  • How to cache method results in .Net

    - by SP
    Using webmethods, caching the results is pretty straight forward using "CacheDuration" attribute. Is there a similar "easy" way to cache non-webmethod outputs (or static methods) based on the parameters? I would appreciate any help. Thanks in advance!

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  • Override to_json in Rails 2.3.5

    - by smotchkkiss
    I've seen some other examples on SO, but I none do what I'm looking for. I'm trying: class User < ActiveRecord::Base def to_json super(:only => :username, :methods => [:foo, :bar]) end end I'm getting ArgumentError: wrong number of arguments (1 for 0). Any ideas?

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  • Javascript static method intheritance

    - by Matteo Pagliazzi
    I want to create a javascript class/object that allow me to have various method: Model class Model.all() » static method Model.find() » static method Model delete() » instance method Model save() » instance method Model.create() » static that returns a new Model instance For static method I can define them using: Model.staticMethod(){ method } while for instance method is better to use: function Model(){ this.instanceMethod = function(){} } and then create a new instance or using prototype? var m = function Model(){ } m.prototype.method() = function(){ } Now let's say that I want to create a new class based on Model, how to inherit not only its prototypes but also its static methods?

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  • Bad method names and what it says about code structure.

    - by maxfridbe
    (Apologies in advance if this is a re-post but I didn't find similar posts) What bad method name patterns have you seen in code and what did it tell you about the code. For instance, I keep seeing: public void preform___X___IfNecessary(...); I believe that this is bad because the operation X has an inversion of conditions. Note that this is a public method because classes methods might legitimately require private helpers like this

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  • functional test for rails controller private method

    - by mohit
    I have a private method in my controller. which is used for some database update. this method i am calling from another controller method. and it works fine. But when i am trying to write a test case for that method then It is tripping on accessing (session variable and params) in my functional all other methods are working fine the problem is only with private method? In my setup method in functional test, I am setting session also.?

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  • functional test for rails controller privaet method

    - by mohit
    I have a private method in my controller. which is used for some database update. this method i am calling from another controller method. and it works fine. But when i am trying to write a test case for that method then It is tripping on accessing (session variable and params) in my functional all other methods are working fine the problem is only with private method? In my setup method in functional test, I am setting session also.?

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  • What is the best way to return two values from a method?

    - by Edward Tanguay
    When I have to write methods which return two values, I usually go about it as in the following code which returns a List<string>. Or if I have to return e.g. a id and string, then I return a List<object> and then pick them out with index number and recast the values. This recasting and referencing by index seems inelegant so I want to develop a new habit for methods that return two values. What is the best pattern for this? using System; using System.Collections.Generic; using System.Linq; namespace MultipleReturns { class Program { static void Main(string[] args) { string extension = "txt"; { List<string> entries = GetIdCodeAndFileName("first.txt", extension); Console.WriteLine("{0}, {1}", entries[0], entries[1]); } { List<string> entries = GetIdCodeAndFileName("first", extension); Console.WriteLine("{0}, {1}", entries[0], entries[1]); } Console.ReadLine(); } /// <summary> /// gets "first.txt", "txt" and returns "first", "first.txt" /// gets "first", "txt" and returns "first", "first.txt" /// it is assumed that extensions will always match /// </summary> /// <param name="line"></param> public static List<string> GetIdCodeAndFileName(string line, string extension) { if (line.Contains(".")) { List<string> parts = line.BreakIntoParts("."); List<string> returnItems = new List<string>(); returnItems.Add(parts[0]); returnItems.Add(line); return returnItems; } else { List<string> returnItems = new List<string>(); returnItems.Add(line); returnItems.Add(line + "." + extension); return returnItems; } } } public static class StringHelpers { public static List<string> BreakIntoParts(this string line, string separator) { if (String.IsNullOrEmpty(line)) return null; else { return line.Split(new string[] { separator }, StringSplitOptions.None).Select(p => p.Trim()).ToList(); } } } }

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  • Calling javascript method from from inside object

    - by John
    I am struggling with methods in JavaScript. obj = function(){ this.getMail = function getMail (){ } //Here I would like to run the get mail once but this.getMail() or getMail() wont work } var mail = new obj(); mail.getMail(); How do I make the method in a way that I can run it both inside the object and from the outside Thanks

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  • I need to modify a program to use arrays and a method call. Should I modify the running file, the data collection file, or both?

    - by g3n3rallyl0st
    I have to have multiple classes for this program. The problem is, I don't fully understand arrays and how they work, so I'm a little lost. I will post my program I have written thus far so you can see what I'm working with, but I don't expect anyone to DO my assignment for me. I just need to know where to start and I'll try to go from there. I think I need to use a double array since I will be working with decimals since it deals with money, and my method call needs to calculate total price for all items entered by the user. Please help: RUNNING FILE package inventory2; import java.util.Scanner; public class RunApp { public static void main(String[] args) { Scanner input = new Scanner( System.in ); DataCollection theProduct = new DataCollection(); String Name = ""; double pNumber = 0.0; double Units = 0.0; double Price = 0.0; while(true) { System.out.print("Enter Product Name: "); Name = input.next(); theProduct.setName(Name); if (Name.equalsIgnoreCase("stop")) { return; } System.out.print("Enter Product Number: "); pNumber = input.nextDouble(); theProduct.setpNumber(pNumber); System.out.print("Enter How Many Units in Stock: "); Units = input.nextDouble(); theProduct.setUnits(Units); System.out.print("Enter Price Per Unit: "); Price = input.nextDouble(); theProduct.setPrice(Price); System.out.print("\n Product Name: " + theProduct.getName()); System.out.print("\n Product Number: " + theProduct.getpNumber()); System.out.print("\n Amount of Units in Stock: " + theProduct.getUnits()); System.out.print("\n Price per Unit: " + theProduct.getPrice() + "\n\n"); System.out.printf("\n Total cost for %s in stock: $%.2f\n\n\n", theProduct.getName(), theProduct.calculatePrice()); } } } DATA COLLECTION FILE package inventory2; public class DataCollection { String productName; double productNumber, unitsInStock, unitPrice, totalPrice; public DataCollection() { productName = ""; productNumber = 0.0; unitsInStock = 0.0; unitPrice = 0.0; } //setter methods public void setName(String name) { productName = name; } public void setpNumber(double pNumber) { productNumber = pNumber; } public void setUnits(double units) { unitsInStock = units; } public void setPrice(double price) { unitPrice = price; } //getter methods public String getName() { return productName; } public double getpNumber() { return productNumber; } public double getUnits() { return unitsInStock; } public double getPrice() { return unitPrice; } public double calculatePrice() { return (unitsInStock * unitPrice); } }

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  • Java: Cannot find a method's symbol even though that method is declared later in the class. The remaining code is looking for a class.

    - by Midimistro
    This is an assignment that we use strings in Java to analyze a phone number. The error I am having is anything below tester=invalidCharacters(c); does not compile because every line past tester=invalidCharacters(c); is looking for a symbol or the class. In get invalidResults, all I am trying to do is evaluate a given string for non-alphabetical characters such as *,(,^,&,%,@,#,), and so on. What to answer: Why is it producing an error, what will work, and is there an easier method WITHOUT using regex. Here is the link to the assignment: http://cis.csuohio.edu/~hwang/teaching/cis260/assignments/assignment9.html public class PhoneNumber { private int areacode; private int number; private int ext; /////Constructors///// //Third Constructor (given one string arg) "xxx-xxxxxxx" where first three are numbers and the remaining (7) are numbers or letters public PhoneNumber(String newNumber){ //Note: Set default ext to 0 ext=0; ////Declare Temporary Storage and other variables//// //for the first three numbers String areaCodeString; //for the remaining seven characters String newNumberString; //For use in testing the second half of the string boolean containsLetters; boolean containsInvalid; /////Separate the two parts of string///// //Get the area code part of the string areaCodeString=newNumber.substring(0,2); //Convert the string and set it to the area code areacode=Integer.parseInt(areaCodeString); //Skip the "-" and Get the remaining part of the string newNumberString=newNumber.substring(4); //Create an array of characters from newNumberString to reuse in later methods for int length=newNumberString.length(); char [] myCharacters= new char [length]; int i; for (i=0;i<length;i++){ myCharacters [i]=newNumberString.charAt(i); } //Test if newNumberString contains letters & converting them into numbers String reNewNumber=""; //Test for invalid characters containsInvalid=getInvalidResults(newNumberString,length); if (containsInvalid==false){ containsLetters=getCharResults(newNumberString,length); if (containsLetters==true){ for (i=0;i<length;i++){ myCharacters [i]=(char)convertLetNum((myCharacters [i])); reNewNumber=reNewNumber+myCharacters[i]; } } } if (containsInvalid==false){ number=Integer.parseInt(reNewNumber); } else{ System.out.println("Error!"+"\t"+newNumber+" contains illegal characters. This number will be ignored and skipped."); } } //////Primary Methods/Behaviors/////// //Compare this phone number with the one passed by the caller public boolean equals(PhoneNumber pn){ boolean equal; String concat=(areacode+"-"+number); String pN=pn.toString(); if (concat==pN){ equal=true; } else{ equal=false; } return equal; } //Convert the stored number to a certain string depending on extension public String toString(){ String returned; if(ext==0){ returned=(areacode+"-"+number); } else{ returned=(areacode+"-"+number+" ext "+ext); } return returned; } //////Secondary Methods/////// //Method for testing if the second part of the string contains any letters public static boolean getCharResults(String newNumString,int getLength){ //Recreate a character array int i; char [] myCharacters= new char [getLength]; for (i=0;i<getLength;i++){ myCharacters [i]=newNumString.charAt(i); } boolean doesContainLetter=false; int j; for (j=0;j<getLength;j++){ if ((Character.isDigit(myCharacters[j])==true)){ doesContainLetter=false; } else{ doesContainLetter=true; return doesContainLetter; } } return doesContainLetter; } //Method for testing if the second part of the string contains any letters public static boolean getInvalidResults(String newNumString,int getLength){ boolean doesContainInvalid=false; int i; char c; boolean tester; char [] invalidCharacters= new char [getLength]; for (i=0;i<getLength;i++){ invalidCharacters [i]=newNumString.charAt(i); c=invalidCharacters [i]; tester=invalidCharacters(c); if(tester==true)){ doesContainInvalid=false; } else{ doesContainInvalid=true; return doesContainInvalid; } } return doesContainInvalid; } //Method for evaluating string for invalid characters public boolean invalidCharacters(char letter){ boolean returnNum=false; switch (letter){ case 'A': return returnNum; case 'B': return returnNum; case 'C': return returnNum; case 'D': return returnNum; case 'E': return returnNum; case 'F': return returnNum; case 'G': return returnNum; case 'H': return returnNum; case 'I': return returnNum; case 'J': return returnNum; case 'K': return returnNum; case 'L': return returnNum; case 'M': return returnNum; case 'N': return returnNum; case 'O': return returnNum; case 'P': return returnNum; case 'Q': return returnNum; case 'R': return returnNum; case 'S': return returnNum; case 'T': return returnNum; case 'U': return returnNum; case 'V': return returnNum; case 'W': return returnNum; case 'X': return returnNum; case 'Y': return returnNum; case 'Z': return returnNum; default: return true; } } //Method for converting letters to numbers public int convertLetNum(char letter){ int returnNum; switch (letter){ case 'A': returnNum=2;return returnNum; case 'B': returnNum=2;return returnNum; case 'C': returnNum=2;return returnNum; case 'D': returnNum=3;return returnNum; case 'E': returnNum=3;return returnNum; case 'F': returnNum=3;return returnNum; case 'G': returnNum=4;return returnNum; case 'H': returnNum=4;return returnNum; case 'I': returnNum=4;return returnNum; case 'J': returnNum=5;return returnNum; case 'K': returnNum=5;return returnNum; case 'L': returnNum=5;return returnNum; case 'M': returnNum=6;return returnNum; case 'N': returnNum=6;return returnNum; case 'O': returnNum=6;return returnNum; case 'P': returnNum=7;return returnNum; case 'Q': returnNum=7;return returnNum; case 'R': returnNum=7;return returnNum; case 'S': returnNum=7;return returnNum; case 'T': returnNum=8;return returnNum; case 'U': returnNum=8;return returnNum; case 'V': returnNum=8;return returnNum; case 'W': returnNum=9;return returnNum; case 'X': returnNum=9;return returnNum; case 'Y': returnNum=9;return returnNum; case 'Z': returnNum=9;return returnNum; default: return 0; } } } Note: Please Do not use this program to cheat in your own class. To ensure of this, I will take this question down if it has not been answered by the end of 2013, if I no longer need an explanation for it, or if the term for the class has ended.

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