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I'm trying to create a cipher in C#, I need to take in the encrypted text from a text document and have the decryptions show up in the console and have the correct one export to a text document.

This is what I have so far:

C#
using System;
using System.IO;

public class cipher
{
    public static void Main(string[] args)
    {

        string output = "";
        int shift;
        bool userright = false;
        string cipher = File.ReadAllText("decryptme.txt");

        char[] decr = cipher.ToCharArray();

        do {

            Console.WriteLine("How many times would you like to shift? (Between 0 and 26)");
            shift = Convert.ToInt32(Console.ReadLine());
            if (shift > 26) {
                Console.WriteLine("Over the limit");
                userright = false;
            }
            if (shift < 0) {
                Console.WriteLine("Under the limit");
                userright = false;
            }
            if (shift <= 26 && shift >= 0)
            {
                userright = true;
            }
        }


        while (userright == false);


        for (int i = 0; i < decr.Length; i++)
        {
         
            {
            char character = decr[i];

            character = (char)(character + shift);

            if (character == '\'' || character == ' ')
                continue;

            if (character > 'Z')
                character = (char)(character - 26);
                
            else if (character < 'A')
                character = (char)(character + 26);
               

              output = output + character;
            }

            Console.WriteLine("\nShift {0} \n {1}", i + 1, output);
        }

        StreamWriter file = new StreamWriter("decryptedtext.txt");
		file.WriteLine(output);
		file.Close();

   	}
}


I'm stuck right now, I have it feed in the encrypted text but it doesn't decipher it. It just prints in the console the encrypted text. Any help would be appreciated.

Thanks.
Posted
Updated 21-Apr-22 1:09am
Comments
PIEBALDconsult 15-Dec-15 8:55am
   
0) cipher.ToCharArray(); --- Is needless, a string is already indexable.
1) Convert.ToInt32(Console.ReadLine()); --- Don't use Convert; use Int32.TryParse .
2) All three if (shift statements can be replaced with one userright = (shift <= 26 && shift >= 0) statement.
3) For output, use a StringBuilder rather than a string.

BillWoodruff 15-Dec-15 11:52am
   
In the last few months there have been several questions posted about the Casear Cipher, and there's lots good solutions, and code.

http://www.codeproject.com/search.aspx?q=%22caesar+cipher%22&doctypeid=4%3b5&sort=createddesc

Try this link.
   
Start by feeding it "known" text: assume a shift of one and the text "HELLO"
Create a text file using NotePad that contains just "IFMMP" and save it.
Put a breakpoint on the line:
C#
char character = decr[i];

And run your app, feeding it the text file you just created.
Then step through your program one line at a time, and look at exactly what is going on.
The first line should fetch the encrypted character, the next should decrypt it - so you shown be able to see the decrypted character in the debugger.
It should be immediately obvious what the problem is! :laugh:

Hint: you won't need to go far to spot the problem...
   
This is a bit simpler. Uses mod to deal with numbers outside bounds:

C#
private abstract class CharClass
{
    //default shift
    private static int _shift = 13;
    //chars that can be shifted
    private const string Alphabet = "abcdefghijklmnopqrstuvwxyz";

    //update the shift number
    public static int Shift
    {
        private get { return _shift; }
        set { _shift = value; }
    }

    //perform the shift per char
    public static char ShiftChar(char c)
    {
        var index = Alphabet.IndexOf(c);
        if (index == -1)
            return c;
        index = ((index + Shift) + Alphabet.Length) % Alphabet.Length;
        return Alphabet[index];
    }

    //perform the shift on a string
    public static string ShiftString(string s)
    {
        return new string(s.Select(ShiftChar).ToArray());
    }

}


usage: (well, my test method)

C#
[TestMethod]
public void Test1()
{
    CharClass.Shift = 5;

    const string unEncrypted = "the quick brown fox jumps over the lazy dog";

    var encrypted = CharClass.ShiftString(unEncrypted);

    CharClass.Shift = -5;

    var unEncryptedAgain = CharClass.ShiftString(encrypted);

    Assert.IsFalse(unEncrypted.Equals(encrypted));
    Assert.IsFalse(encrypted.Equals(unEncryptedAgain));
    Assert.IsTrue(unEncrypted.Equals(unEncryptedAgain));
}


NB:
ONLY the chars in Alphabet will be shifted. uppercase chars will not in this case, neither will whitespace or special chars.

I could update this to handle upper case too, but I'm sure you can manage it ^_^

Hope that helps
Andy
   
Quote:
char[] enc = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z' };
char[] dec = { 'z', 'y', 'x', 'w', 'v', 'u', 't', 's', 'r', 'q', 'p', 'o', 'n', 'm', 'l', 'k', 'j', 'i', 'h', 'g', 'f', 'e', 'd', 'c', 'b', 'a' };
Console.WriteLine("Enter Massge");
string x = Console.ReadLine();
Console.WriteLine("Inter Key Number");
int qq = Convert.ToInt32(Console.ReadLine());
//-----------------------

char[] main = x.ToCharArray();
for (int i = 0; i < main.Length; i++)
{
for (int j = 0; j < enc.Length; j++)
{
if (main[i] == enc[j])
{
Console.Write(dec[j=qq]);
}
}
}
   
Comments
Dave Kreskowiak 21-Apr-22 7:46am
   
Doing someone's homework for them is never a good idea.

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