3. Write a function named caesarDecipher that accepts a key value (the Caesar sh

Question

3. Write a function named caesarDecipher that accepts a key value (the Caesar shift value) as its first command-line parameter, and a string (the ciphertext) for its second parameter. Your caesarDecipher function should look like this:

caesarDecipher (shift, ciphertext):

''Returns plaintext obtained by transforming every letter in the ciphertext by a Caesar cipher by

the specified shift. Non-letter characters should remain unchanged in the plaintext.''

[Your code goes here]

return [something]

Testing

To see if your code works properly, you should first try to encrypt and then decrypt a given message, and make sure it does it right.

Here are a few things for you to try to decrypt. Note that non-letters (spaces and the single quote) are copied as-is to the ciphertext.

"gduwk ydghu lv oxnh vnbzdonhu'v idwkhu" (key is 3)

"v fnirq n ybg ba zl nhgb vafhenapr ol fjvgpuvat gb trvxb" (key is 13)

Explanation / Answer

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace caesar

{

class Program

{

// the function is valid only for lowercase characters

public string caesarDecipher(int shift, string cipherText)

{

string text1 = "";

int x;

for (int i = 0; i < cipherText.Length; i++)

{

if (cipherText[i] >= 97 && cipherText[i] <= 123)

{

x = (int)(cipherText[i] - shift);

if (x < 97) // accounting for when ASCII values are less than that of a

x = 123 - (97 - x);

text1 += (char)x;

}

else

text1 += cipherText[i];

}

return text1;

}

static void Main(string[] args)

{

Program p1 = new Program();

Console.WriteLine("enter text to decipher:");

string s2 = Console.ReadLine();

Console.WriteLine("enter key");

int key2 = int.Parse(Console.ReadLine());

string mods2 = p1.caesarDecipher(key2, s2);

Console.WriteLine(" " + mods2);

}

}

}

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