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  • Unable to reverse seemingly simple rails migration - getting "altered_table.column may not be NULL"

    - by brad
    I have a table 'invoices' in my development database (sqlite3) populated with a small amount of test data. I wanted to add a column 'invoice_number' to it and set up a migration like so: class AddInvoiceNumberColumnToInvoices < ActiveRecord::Migration def self.up add_column :invoices, :invoice_number, :integer end def self.down remove_column :invoices, :invoice_number end end I ran rake db:migrate and it seemed to migrate just fine. However, when I tried to access this column through ActiveRecord it didn't seem to be there. I decided to undo this migration and try again (not sure what I was going to try but I thought I'd start by undoing it) with rake db:migrate VERSION='whatever_the_migration_before_this_one_was_called'. This failed with the error message == AddInvoiceNumberColumnToInvoices: reverting =============================== -- remove_column(:invoices, :invoice_number) rake aborted! An error has occurred, this and all later migrations canceled: altered_invoices.invoice_number may not be NULL I can't find any documentation of this error. Is anyone able to explain what I have done wrong, and more importantly how I can fix this?

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  • .NET and Closing MSSQL connections

    - by user307076
    I am having a hard time figuring out why the following constructor will not close connnections. When I view the active connections. Here is the code that I have. Public Sub New(ByVal UserID As Integer) Dim oConn As New SqlConnection(ConfigurationManager.ConnectionStrings("connStr").ToString()) Dim cmd As New SqlCommand("stored proc", oConn) Dim sdr As SqlDataReader cmd.CommandType = CommandType.StoredProcedure cmd.Parameters.AddWithValue("@userID", UserID) oConn.Open() sdr = cmd.ExecuteReader() Try If Not sdr.HasRows Then sdr.Close() If Not oConn Is Nothing Then If oConn.State <> ConnectionState.Closed Then oConn.Close() End If End If cmd.Dispose() Exit Sub End If 'User has account in WATS, proceed to load account information While sdr.Read _firstname = Convert.ToString(sdr("First Name")) _lastname = Convert.ToString(sdr("Last Name")) End While Catch ex As Exception 'Throw New Exception("User Error: " + ex.Message) Finally sdr.Close() If Not oConn Is Nothing Then If oConn.State <> ConnectionState.Closed Then oConn.Close() End If End If cmd.Dispose() End Try End Sub

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  • If the UIApplicationMain() never returns then when does the autorelease pool gets released?

    - by sid
    For code: int main(int argc, char *argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; int retVal = UIApplicationMain(argc, argv, nil, nil); [pool release]; return retVal; } Apple's doc clearly specifies: Return Value: Even though an integer return type is specified, this function never returns. When users terminate an iPhone application by pressing the Home button, the application immediately exits by calling the exit system function with an argument of zero. Secondly, in int UIApplicationMain ( int argc, char *argv[], NSString *principalClassName, NSString *delegateClassName ); how can we access the argv from our UIApplication subclass?

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  • How to make Databinding type safe and support refactoring

    - by Ian Ringrose
    When I wish to bind a control to a property of my object, I have to provide the name of the property as a string. This is not very good because: If the property is removed or renamed, I don’t get a compiler warning. If a rename the property with a refactoring tool, it is likely the data binding will not be updated. I don’t get an error until runtime if the type of the property is wrong, e.g. binding an integer to a date chooser. Is there a design-paten that gets round this, but still has the ease of use of data-binding? (This is a problem in WinForm, Asp.net and WPF and most likely lots of other systems) I have now found "workarounds for nameof() operator in C#: typesafe databinding" that also has a good starting point for a solution.

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  • What is a convenient base for a bignum library & primality testing algorithm?

    - by nn
    Hi, I am to program the Solovay-Strassen primality test presented in the original paper on RSA. Additionally I will need to write a small bignum library, and so when searching for a convenient representation for bignum I came across this [specification][1]: struct { int sign; int size; int *tab; } bignum; I will also be writing a multiplication routine using the Karatsuba method. So, for my question: What base would be convenient to store integer data in the bignum struct? Note: I am not allowed to use third party or built-in implementations for bignum such as GMP. Thank you.

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  • Objective C - RegexKitLite - Parsing inner contents of a string, ie: start(.*?)end

    - by Stu
    Please consider the following: NSString *myText = @"mary had a little lamb"; NSString *regexString = @"mary(.*?)little"; for)NSString *match in [myText captureComponentsMatchedByRegex:regexString]){ NSLog(@"%@",match); } This will output to the console two things: 1) "mary had a little" 2) "had a" What I want is just the 2nd bit of information "had a". Is there is a way of matching a string and returning just the inner part? I'm fairly new to Objective C, this feels a rather trivial question yet I can't find a less messy way of doing this than incrementing an integer in the for loop and on the second iteration storing the "had a" in an NSString.

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  • How to use derived class shared variables in shared methods of base class

    - by KoolKabin
    Hi guys, I am trying to add shared members in derived classes and use that values in base classes... I have base class DBLayer public shared function GetDetail(byval UIN as integer) dim StrSql = string.format("select * from {0} where uin = {1}", tablename, uin) .... end function end class my derived class class User inherits dblayer public shared tabledname as string = "users" end class class item inherits dblayer public shared tabledname as string = "item" end class class category inherits dblayer public shared tabledname as string = "category" end class currently there is error using the tablename variable of derived class in base class but i want to use it... coz i dun know other techniques... if other solutions are better then u can post it or u can say how can i make it work? confused...

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  • PHP 5.2.12 - Interesting Switch Statement Bug With Integers and Strings

    - by Levi Hackwith
    <?php $var = 0; switch($var) { case "a": echo "I think var is a"; break; case "b": echo "I think var is b"; break; case "c": echo "I think var is c"; break; default: echo "I know var is $var"; break; } ?> Maybe someone else will find this fascinating and have an answer. If you run this, it outputs I think the var is a when clearly it's 0. Now, I'm most certain this has something to do with the fact that we're using strings in our switch statement but the variable we're checking is an integer. Does anyone know why PHP behaves this way? It's nothing too major, but it did give me a bit of a headache today. Thanks folks!

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  • md5 hash for file without File Attributes

    - by Glennular
    Using the following code to compute MD5 hashs of files: Private _MD5Hash As String Dim md5 As New System.Security.Cryptography.MD5CryptoServiceProvider Dim md5hash() As Byte md5hash = md5.ComputeHash(Me._BinaryData) Me._MD5Hash = ByteArrayToString(md5hash) Private Function ByteArrayToString(ByVal arrInput() As Byte) As String Dim sb As New System.Text.StringBuilder(arrInput.Length * 2) For i As Integer = 0 To arrInput.Length - 1 sb.Append(arrInput(i).ToString("X2")) Next Return sb.ToString().ToLower End Function We are getting different hashes depending on the create-date and modify-date of the file. We are storing the hash and the binary file in a SQL DB. This works fine when we upload the same instance of a file. But when we save a new instance of the file from the DB (with today's date as the create/modify) on the file-system and then check the new hash versus the MD5 stored in the DB they do not match, and therefor fail a duplicate check. How can we check for a file hash excluding the file attributes? or is there a different issue here?

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  • How are integers converted to strings under the hood?

    - by CrazyJugglerDrummer
    I suppose the real question is how to convert base2/binary to base10. The most common application of this would probably be in creating strings for output: turning a chunk of binary numerical data into an array of characters. How exactly is this done? my guess: Seeing as there probably isn't a string predefined for each numerical value, I'm guessing that the computer goes through each bit of the integer from right to left, each time incrementing the appropriate values in the char array/base10 notation places. If we take the number 160 in binary (10100000), it would know that a 1 in the 8th place means 128, so it places 1 into the third column, 2 in the second, and 8 in the third. The 1 in the 6th column means 32, and it would add those values to the second and first place, carrying over if needed. After this it's an easy conversion to actual char codes.

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  • Advantage of using a static member function instead of an equivalent non-static member function?

    - by jonathanasdf
    I was wondering whether there's any advantages to using a static member function when there is a non-static equivalent. Will it result in faster execution (because of not having to care about all of the member variables), or maybe less use of memory (because of not being included in all instances)? Basically, the function I'm looking at is an utility function to rotate an integer array representing pixel colours an arbitrary number of degrees around an arbitrary centre point. It is placed in my abstract Bullet base class, since only the bullets will be using it and I didn't want the overhead of calling it in some utility class. It's a bit too long and used in every single derived bullet class, making it probably not a good idea to inline. How would you suggest I define this function? As a static member function of Bullet, of a non-static member function of Bullet, or maybe not as a member of Bullet but defined outside of the class in Bullet.h? What are the advantages and disadvantages of each?

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  • DataAnnotations in ASP.NET MVC 2 - Stop MVC from applying RequiredAttribute to Non-nullable DateTime

    - by jwwishart
    Im trying to create a custom version of the RequiredAttribute to replace the built in one and I've got it working for properties that have strings values, but with properties that are DateTime or integer for example, the default RequiredAttribute seems to be applied automatically (IF the property is not nullable!) My problem is that i want to be able to specify a DateTime property as required using my custom required validator which gets the error message from a resources file (I don't want to have to tell the RequiredAttribute the type of the resource file and the key every time i apply it. That is why I'm making a custom one.) How can i prevent the framework from applying the required attribute to properties of type DateTime and int etc without changing them to nullable. Thanks

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  • Function pointer arrays in Fortran

    - by Eduardo Dobay
    I can create function pointers in Fortran 90, with code like real, external :: f and then use f as an argument to another function/subroutine. But what if I want an array of function pointers? In C I would just do double (*f[])(int); to create an array of functions returning double and taking an integer argument. I tried the most obvious, real, external, dimension(3) :: f but gfortran doesn't let me mix EXTERNAL and DIMENSION. Is there any way to do what I want? (The context for this is a program for solving a system of differential equations, so I could input the equations without having a million parameters in my subroutines.)

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  • Patterns for simulating optional "out" parameters in C#?

    - by Jesse McGrew
    I'm translating an API from C to C#, and one of the functions allocates a number of related objects, some of which are optional. The C version accepts several pointer parameters which are used to return integer handles to the objects, and the caller can pass NULL for some of the pointers to avoid allocating those objects: void initialize(int *mainObjPtr, int *subObjPtr, int *anotherSubObjPtr); initialize(&mainObj, &subObj, NULL); For the C# version, the obvious translation would use out parameters instead of pointers: public static void Initialize(out int mainObj, out int subObj, out int anotherSubObj); ... but this leaves no way to indicate which objects are unwanted. Are there any well-known examples of C# APIs doing something similar that I could imitate? If not, any suggestions?

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  • Multiple forms in delphi

    - by Hendriksen123
    In my Delphi Project i want to have a 'Settings' button that when clicked, opens a second form (i think this is the correct term, i essentially want a new window to open) for settings. When the user has finished changing the settings on this new form, i want the form to close on a button click. The settings the user types in will also need to be accessible to the first, 'main' form. So, for example, if my programme consisted of a main form, that calculated 'A' + 'B' (A and B being integer variables), with the settings form allowing the user to set values for A and B, how would i do this?

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  • Good input validation loop using cin - C++

    - by Alex
    Hi there, I'm in my second OOP class, and my first class was taught in C#, so I'm new to C++ and currently I am practicing input validation using cin. So here's my question: Is this loop I constructed a pretty good way of validating input? Or is there a more common/accepted way of doing it? Thanks! Code: int taxableIncome; int error; // input validation loop do { error = 0; cout << "Please enter in your taxable income: "; cin >> taxableIncome; if (cin.fail()) { cout << "Please enter a valid integer" << endl; error = 1; cin.clear(); cin.ignore(80, '\n'); } }while(error == 1);

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  • How to import text file to table with primary key as auto-increment

    - by webworm
    I have some bulk data in a text file that I need to import into a MySQL table. The table consists of two fields .. ID (integer with auto-increment) Name (varchar) The text file is a large collection of names with one name per line ... (example) John Doe Alex Smith Bob Denver I know how to import a text file via phpMyAdmin however, as far as I understand, I need to import data that has the same number of fields as the target table. Is there a way to import the data from my text file into one field and have the ID field auto-increment automatically? Thank you in advance for any help.

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  • 256 colors, foreground and background

    - by push.cx
    This is a tale of two scripts and is related to a previous question. The two scripts are at http://gist.github.com/50692. The ansi.rb script displays all 256 colors on all 256 background colors. The ncurses.rb script displays all 256 foreground colors but the background displays the basic 16 and then seems to cycle through various attributes like blinking and reverse video. So what gives? Is this the bug in ncurses that it uses a signed integer for color pairs? (ie 'tput colors' says 256 but 'tput pairs' says 32767 instead 65536) It seems like if that were the case the first half of the colors pairs would display properly but the second half would repeat or get into the attributes as the int wraps.

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  • Querying a Single Column with LINQ

    - by Hossein Margani
    Hi Every one! I want to fetch array of values of a single column in a table, for example, I have a table named Customer(ID,Name), and want to fetch ids of all customers. my query in LINQ is: var ids = db.Customers.Select(c=>c.ID).ToList(); The answer of this query is correct, but I ran SQL Server Profiler, and saw the query which was like this: SELECT [t0].[ID], [t0].[Name] FROM [dbo].[Customer] AS [t0] I understood that LINQ selects all columns and then creates the integer array of ID fields. How can I write a LINQ query which generates this query in SQL Server: SELECT [t0].[ID] FROM [dbo].[Customer] AS [t0] Thank you.

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  • Rationale behind Python's preferred for syntax

    - by susmits
    What is the rationale behind the advocated use of the for i in xrange(...)-style looping constructs in Python? For simple integer looping, the difference in overheads is substantial. I conducted a simple test using two pieces of code: File idiomatic.py: #!/usr/bin/env python M = 10000 N = 10000 if __name__ == "__main__": x, y = 0, 0 for x in xrange(N): for y in xrange(M): pass File cstyle.py: #!/usr/bin/env python M = 10000 N = 10000 if __name__ == "__main__": x, y = 0, 0 while x < N: while y < M: y += 1 x += 1 Profiling results were as follows: bash-3.1$ time python cstyle.py real 0m0.109s user 0m0.015s sys 0m0.000s bash-3.1$ time python idiomatic.py real 0m4.492s user 0m0.000s sys 0m0.031s I can understand why the Pythonic version is slower -- I imagine it has a lot to do with calling xrange N times, perhaps this could be eliminated if there was a way to rewind a generator. However, with this deal of difference in execution time, why would one prefer to use the Pythonic version?

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  • Why looping in Delphi faster than C#?

    - by isa
    Delphi: procedure TForm1.Button1Click(Sender: TObject); var I,Tick:Integer; begin Tick := GetTickCount(); for I := 0 to 1000000000 do begin end; Button1.Caption := IntToStr(GetTickCount()-Tick)+' ms'; end; C#: private void button1_Click(object sender, EventArgs e) { int tick = System.Environment.TickCount; for (int i = 0; i < 1000000000; ++i) { } tick = System.Environment.TickCount - tick; button1.Text = tick.ToString()+" ms"; } Delphi gives around 515 ms C# gives around 3775 ms

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  • What is the correct way to specify dimensions in DIP from Java code ?

    - by Pavel Lahoda
    Trying to digest docs about design Multiple resolutions (http://d.android.com/guide/practices/screens_support.html#dips-pels) I found that it is possible to set dimensions of my interface elements in XML layouts using DIPs as in following fragment : "android:layout_width="10dip" But all Java interface takes integer as arguments and there is no way to specify dimensions in DIPs. What is the correct way to calculate this ? I figured that I have to use property density of DisplayMetrics class but is this a correct way ? May I relly that formula : pixels * DisplayMetrics.density = dip is always correct ? Will there be API in DIPs for Java ?

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  • improving conversions to binary and back in C#

    - by Saad Imran.
    I'm trying to write a general purpose socket server for a game I'm working on. I know I could very well use already built servers like SmartFox and Photon, but I wan't to go through the pain of creating one myself for learning purposes. I've come up with a BSON inspired protocol to convert the the basic data types, their arrays, and a special GSObject to binary and arrange them in a way so that it can be put back together into object form on the client end. At the core, the conversion methods utilize the .Net BitConverter class to convert the basic data types to binary. Anyways, the problem is performance, if I loop 50,000 times and convert my GSObject to binary each time it takes about 5500ms (the resulting byte[] is just 192 bytes per conversion). I think think this would be way too slow for an MMO that sends 5-10 position updates per second with a 1000 concurrent users. Yes, I know it's unlikely that a game will have a 1000 users on at the same time, but like I said earlier this is supposed to be a learning process for me, I want to go out of my way and build something that scales well and can handle at least a few thousand users. So yea, if anyone's aware of other conversion techniques or sees where I'm loosing performance I would appreciate the help. GSBitConverter.cs This is the main conversion class, it adds extension methods to main datatypes to convert to the binary format. It uses the BitConverter class to convert the base types. I've shown only the code to convert integer and integer arrays, but the rest of the method are pretty much replicas of those two, they just overload the type. public static class GSBitConverter { public static byte[] ToGSBinary(this short value) { return BitConverter.GetBytes(value); } public static byte[] ToGSBinary(this IEnumerable<short> value) { List<byte> bytes = new List<byte>(); short length = (short)value.Count(); bytes.AddRange(length.ToGSBinary()); for (int i = 0; i < length; i++) bytes.AddRange(value.ElementAt(i).ToGSBinary()); return bytes.ToArray(); } public static byte[] ToGSBinary(this bool value); public static byte[] ToGSBinary(this IEnumerable<bool> value); public static byte[] ToGSBinary(this IEnumerable<byte> value); public static byte[] ToGSBinary(this int value); public static byte[] ToGSBinary(this IEnumerable<int> value); public static byte[] ToGSBinary(this long value); public static byte[] ToGSBinary(this IEnumerable<long> value); public static byte[] ToGSBinary(this float value); public static byte[] ToGSBinary(this IEnumerable<float> value); public static byte[] ToGSBinary(this double value); public static byte[] ToGSBinary(this IEnumerable<double> value); public static byte[] ToGSBinary(this string value); public static byte[] ToGSBinary(this IEnumerable<string> value); public static string GetHexDump(this IEnumerable<byte> value); } Program.cs Here's the the object that I'm converting to binary in a loop. class Program { static void Main(string[] args) { GSObject obj = new GSObject(); obj.AttachShort("smallInt", 15); obj.AttachInt("medInt", 120700); obj.AttachLong("bigInt", 10900800700); obj.AttachDouble("doubleVal", Math.PI); obj.AttachStringArray("muppetNames", new string[] { "Kermit", "Fozzy", "Piggy", "Animal", "Gonzo" }); GSObject apple = new GSObject(); apple.AttachString("name", "Apple"); apple.AttachString("color", "red"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.5); GSObject lemon = new GSObject(); apple.AttachString("name", "Lemon"); apple.AttachString("color", "yellow"); apple.AttachBool("inStock", false); apple.AttachFloat("price", (float)0.8); GSObject apricoat = new GSObject(); apple.AttachString("name", "Apricoat"); apple.AttachString("color", "orange"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.9); GSObject kiwi = new GSObject(); apple.AttachString("name", "Kiwi"); apple.AttachString("color", "green"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)2.3); GSArray fruits = new GSArray(); fruits.AddGSObject(apple); fruits.AddGSObject(lemon); fruits.AddGSObject(apricoat); fruits.AddGSObject(kiwi); obj.AttachGSArray("fruits", fruits); Stopwatch w1 = Stopwatch.StartNew(); for (int i = 0; i < 50000; i++) { byte[] b = obj.ToGSBinary(); } w1.Stop(); Console.WriteLine(BitConverter.IsLittleEndian ? "Little Endian" : "Big Endian"); Console.WriteLine(w1.ElapsedMilliseconds + "ms"); } Here's the code for some of my other classes that are used in the code above. Most of it is repetitive. GSObject GSArray GSWrappedObject

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  • Using only alphanumeric characters(a-z) inside toCharArray

    - by Aaron
    Below you will find me using toCharArray in order to send a string to array. I then MOVE the value of the letter using a for statement... for(i = 0; i < letter.length; i++){ letter[i] += (shiftCode); System.out.print(letter[i]); } However, when I use shiftCode to move the value such as... a shifted by -1; I get a symbol @. Is there a way to send the string to shiftCode or tell shiftCode to ONLY use letters? I need it to see my text, like "aaron", and when I use the for statement iterate through a-z only and ignore all symbols and numbers. I THINK it is as simple as... letter=codeWord.toCharArray(a,z); But trying different forms of that and googling it didn't give me any results. Perhaps it has to do with regex or something? Below you will find a complete copy of my program; it works exactly how I want it to do; but it iterates through letters and symbols. I also tried finding instructions online for toCharArray but if there exists any arguments I can't locate them. My program... import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; /* * Aaron L. Jones * CS219 * AaronJonesProg3 * * This program is designed to - * Work as a Ceasar Cipher */ /** * * Aaron Jones */ public class AaronJonesProg3 { static String codeWord; static int shiftCode; static int i; static char[] letter; /** * @param args the command line arguments */ public static void main(String[] args) throws IOException { // Instantiating that Buffer Class // We are going to use this to read data from the user; in buffer // For performance related reasons BufferedReader reader; // Building the reader variable here // Just a basic input buffer (Holds things for us) reader = new BufferedReader(new InputStreamReader(System.in)); // Java speaks to us here / We get it to query our user System.out.print("Please enter text to encrypt: "); // Try to get their input here try { // Get their codeword using the reader codeWord = reader.readLine(); // Make that input upper case codeWord = codeWord.toUpperCase(); // Cut the white space out codeWord = codeWord.replaceAll("\\s",""); // Make it all a character array letter = codeWord.toCharArray(); } // If they messed up the input we let them know here and end the prog. catch(Throwable t) { System.out.println(t.toString()); System.out.println("You broke it. But you impressed me because" + "I don't know how you did it!"); } // Java Speaks / Lets get their desired shift value System.out.print("Please enter the shift value: "); // Try for their input try { // We get their number here shiftCode = Integer.parseInt(reader.readLine()); } // Again; if the user broke it. We let them know. catch(java.lang.NumberFormatException ioe) { System.out.println(ioe.toString()); System.out.println("How did you break this? Use a number next time!"); } for(i = 0; i < letter.length; i++){ letter[i] += (shiftCode); System.out.print(letter[i]); } System.out.println(); /**************************************************************** **************************************************************** ***************************************************************/ // Java speaks to us here / We get it to query our user System.out.print("Please enter text to decrypt: "); // Try to get their input here try { // Get their codeword using the reader codeWord = reader.readLine(); // Make that input upper case codeWord = codeWord.toUpperCase(); // Cut the white space out codeWord = codeWord.replaceAll("\\s",""); // Make it all a character array letter = codeWord.toCharArray(); } // If they messed up the input we let them know here and end the prog. catch(Throwable t) { System.out.println(t.toString()); System.out.println("You broke it. But you impressed me because" + "I don't know how you did it!"); } // Java Speaks / Lets get their desired shift value System.out.print("Please enter the shift value: "); // Try for their input try { // We get their number here shiftCode = Integer.parseInt(reader.readLine()); } // Again; if the user broke it. We let them know. catch(java.lang.NumberFormatException ioe) { System.out.println(ioe.toString()); System.out.println("How did you break this? Use a number next time!"); } for(i = 0; i < letter.length; i++){ letter[i] += (shiftCode); System.out.print(letter[i]); } System.out.println(); } }

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  • How do I randomly fill an array in Java?

    - by Kat
    I'm writing a program that creates a 2D array from a integer n. I then have to fill the array with values from 1 to the n*n array size and check to see if it is a magic square. The way I am doing it now fills the array in order from 1 to n*n array size. How can I make that random? My code: System.out.print("Enter an whole number: "); int n = scan.nextInt(); int [][] magic = new int [n][n]; for (int row = 0; row < magic.length; row++) { for(int col = 0; col < magic[row].length; col++) magic[row][col] = ((row * n) + 1) + col; }

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