Caesar Cypher algorithm (JAVA)

randomx · 10-05-2003, 12:45 PM

This code is supposed to "encrypt" all characters of the sentence you input by shifting it 4 characters down the alphabet.

For example, if I type "angel" it should display "erkip".

But I'm stuck. My code just prints the first "encrypted" character of the sentence. Like if I type "angel" it just prints "e".

I tried everything...like modifying the (char)iteration (last line), variable by adding 4 to it and I get one of those "out of range errors".
In fact, any modification to any other variable gives me the "out of range" errors.

I was wondering if maybe you guys could enlighten me with your wisdom. I think the problem is in the for-loop but I can't figure out exactly where.

I'll post the final code when (if) I get it done. It might be useful to somebody else.

Thanks,

randomX

Code:

public class CaesarCypher
{
	public static final int MOVE_DOWN = 4;
	public static void main(String [] args)
	{

		String plainText;
		int iteration;
		char character;

		System.out.println("Enter a sentence: ");
		plainText = <some custom made method to get input from keyboard>;


		for (iteration = 0; iteration < plainText.length(); iteration++)
		{
			character = plainText.charAt(iteration);  //get characters
			iteration = (char) (character + MOVE_DOWN); //perform shift
			System.out.println("Encrypted sentence is: " + (char)iteration);
		}


	}
}

Jose Muñiz · 10-05-2003, 02:10 PM

I notice you are assigning the result of (char) (character + MOVE_DOWN) to the same variable you use to control your cycle.

Are you sure that's ok? In my opinion, that is the cause why your iteration stops early.

By the way, with this:

Quote:

for (iteration = 0; iteration < plainText.length(); iteration++)
{
character = plainText.charAt(iteration); //get characters
iteration = (char) (character + MOVE_DOWN); //perform shift
System.out.println("Encrypted sentence is: " + (char)iteration);
}

}
}

You will be getting something like:

Encrypted sentence is a
Encrypted sentence is b
Encrypted sentence is c
Encrypted sentence is d

You should try something like:

Code:

 

System.out.print("Encrypted sentence is: " );

for (iteration = 0; iteration < plainText.length(); iteration++)
{
      character = plainText.charAt(iteration); //get characters
      character = (char) (character + MOVE_DOWN); //perform shift
      System.out.print(character);
}

System.out.println();

Now I've only been using Java for like 2 weeks so I'm not sure if I'm correct here

EDIT

Now this is the code I used and its output:

Code:

 
import java.io.*; 


public class CaesarCypher 
{
	public static void main(String args[])
	{
		final int MOVE_DOWN = 4; 
		String plainText = "angel"; 
		char character; 

		System.out.print("Encrypted sentence is: " );

		for (int iteration = 0; iteration < plainText.length(); iteration++)
		{
      			character = plainText.charAt(iteration); //get characters
      			character = (char) (character + MOVE_DOWN); //perform shift
      			System.out.print(character);
		}

		System.out.println(); 
		

	}
}

OUTPUT:

Code:

 
[joseamuniz@localhost Java]$ javac CaesarCypher.java
[joseamuniz@localhost Java]$ java CaesarCypher
Encrypted sentence is: erkip

randomx · 10-05-2003, 08:03 PM

right on!! Thanks man. Thanks to your tips I was able to get it going. Not only that, but it made me realize that my former algorithm was not quite right. Like on the "w" is pointing to "}". It should point to "a".

I modified the "formula", the shift algorithm. I noticed that former formula was not quite right.

by the way...How do I leave spaces in the encrypted sentences instead of putting a character?

anyway...let me show you the NEW for-loop and NEW formula.

Code:

for (int iteration = 0; iteration < plainText.length(); iteration++)
		{
      			character = plainText.charAt(iteration); //get characters
      			character = (char) ('a' + (character - 'a' + MOVE_DOWN) % 26); //perform shift. New formula.

      			System.out.print(character);
		}

		System.out.println(); 

}//closes void main
} //closes class

Now, How do I leave spaces in the encrypted sentences instead of putting a character?

Right now if you input a string like "angels team" , the space gets printed out as an X. A big "x".

It says "erkipwXxieq"
erkip=angel team=xieq space=X

it should say simply "erkip xieq"

How can I keep the spaces?

thanks bro.

eric.r.turner · 10-05-2003, 09:24 PM

Quote:

Originally posted by randomx
Now, How do I leave spaces in the encrypted sentences instead of putting a character?

Check the character before shifting it to make sure it isn't a space. If it is, skip it and move on to the next character:

Code:

for ( int iteration = 0 ; iteration < plainText.length() ; iteration++ ) {

   character = plainText.charAt( iteration );

   if ( character != ' ' ) {
      character = (char) ( 'a' + ( character - 'a' + MOVE_DOWN ) %26 );
   }

   System.out.print(character);
}

Also, when you post messages you can wrap your code in [ CODE] and [ /CODE] tags so that they keep their formatting (and you don't have to add a comment saying "code starts here"). See how nice my posted code looks? You can even go back and edit your previous posts to make your code look good... hint hint.

randomx · 10-05-2003, 10:16 PM

thank you so much bro.

I got it working now.

randomX

PS: your tips on formatting code on my postings are great.