How do I create a C# Caesar Cipher?

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:

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:

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)

[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]);
}
}
}