Caesar Cipher Shift (using alphabet array)

Question

I am currently writing a Caesar Cipher program in C# for my assignment and I am having a problem.

I am approaching this task using an array where I store the whole alphabet and I declare a shift variable which is defined by character index in the array - the iteration of a for loop. The shift calculation is done in a foreach loop, that fetches a character from a string that is read from a text file. Foreach loop is contained within a for loop that iterates to output every possible shift.

However, the problem is that when I try to access the character in an array by a value of my shift variable, the program doesn't seem to access the character I want, it just outputs the same character as in the original string.

This is the code for the program:

using System; 
using System.IO;

public class caesar_shift
{
    public static void Main()
    {
        string file = @"C:\Users\terasss2\Desktop\Programming and Data Structures\caesarShiftEncodedText.txt";      //String variable that stores a file location
        string encrypted_text = File.ReadAllText(file);     //String variable that contains the text from a file. To get the text, the method in a class SystemIO is ran to read the text. It expects a parameter, which is a file directory.
        string decoded_text = " ";
        int shift = 0;
        char character = '0';

        char[] alphabet = new char[26]{'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'};

        Console.WriteLine("The encrypted text is \n{0}", encrypted_text);       //Display the encrypted text

        for(int i = 0; i < alphabet.Length; i++)        //Start a loop which will display 25 different candidates of decipher
        {
            foreach(char c in encrypted_text)
            {
                character = c;

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

                shift = Array.IndexOf(alphabet, character) - i;     //Define a shift which is the index of a character in an alphabet array, take away the itteration of this loop. Store the result in a variable

                if(shift <= 0)
                    shift = shift + 26;

                if(shift >= 26)
                    shift = shift - 26;

                character = alphabet[shift];    //Set the character to a shifted letter by accessing the array element of a value shift

                Console.WriteLine(character);

                decoded_text = decoded_text + character; 
             }  

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

         }
       }
}

Answer 1

I played a bit with your code. The following gives you the solution, but you have to take care: you couldonly use capital letters, because theres a difference in upper and lower charts. I used the ToUpper() method. Works fine for me. I think that's what your problem was.

public static void Main()
    {
        string encrypted_text = "BCD";     //String variable that contains the text from a file. To get the text, the method in a class SystemIO is ran to read the text. It expects a parameter, which is a file directory.
        string decoded_text = " ";
        int shift = 0;
        char character = '0';
        encrypted_text = encrypted_text.ToUpper();

        char[] alphabet = new char[26] { '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' };

        Console.WriteLine("The encrypted text is \n{0}", encrypted_text);       //Display the encrypted text

        for (int i = 0; i < alphabet.Length; i++)        //Start a loop which will display 25 different candidates of decipher
        {
            decoded_text = "";
            foreach (char c in encrypted_text)
            {
                character = c;

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

                shift = Array.IndexOf(alphabet, character) - i;     //Define a shift which is the index of a character in an alphabet array, take away the itteration of this loop. Store the result in a variable
                if (shift <= 0)
                    shift = shift + 26;

                if (shift >= 26)
                    shift = shift - 26;


                decoded_text += alphabet[shift];
            }
            Console.WriteLine("\nShift {0} \n {1}", i + 1, decoded_text);
        }
    }