CareerCup

Solution:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace MSIntervewPreparation
{
    class CaesarCipherAlgorithm
    {
        private static int shift = 3;

        static void Main(string[] args)
        {
            //Caesar cipher
            string stringToEncrypt = "the quick brown fox jumps over the lazy dog";
            Console.WriteLine("\nThe String To Encrypt: " + stringToEncrypt);

            string encryptedString = Encrypt(stringToEncrypt);

            Console.WriteLine("\nThe resultant Encrypted string is: " + encryptedString);

            Console.WriteLine("\nThe String To Decrypt: " + encryptedString);

            string decryptedString = Decrypt(encryptedString);

            Console.WriteLine("\nThe resultant Decrypted string is: " + decryptedString);
            Console.WriteLine();
        }

        private static string Decrypt(string stringToDecrypt)
        {
            StringBuilder decryptedString = new StringBuilder();
            foreach (char ch in stringToDecrypt)
            {
                int asciiCH;
                char decryptedChar;
                if (char.IsLower(ch))
                {
                    asciiCH = ((int)ch - (int)'a' - shift) % 26;
                    if (asciiCH < 0) asciiCH += 26;
                    decryptedChar = (char)(asciiCH + (int)'a');
                }
                else
                {
                    if (char.IsUpper(ch))
                    {
                        asciiCH = ((int)ch - (int)'A' - shift) % 26;
                        if (asciiCH < 0) asciiCH += 26;
                        decryptedChar = (char)(asciiCH + (int)'A');
                    }
                    else
                    {
                        decryptedChar = ch;
                    }
                }
                decryptedString.Append(decryptedChar.ToString());
            }
            return decryptedString.ToString();
        }

        private static string Encrypt(string stringToEncrypt)
        {
            StringBuilder encryptedString = new StringBuilder();
            foreach (char ch in stringToEncrypt)
            {
                int asciiCH;
                char encryptedChar;
                if (char.IsLower(ch))
                {
                    asciiCH = ((int)ch - (int)'a' + shift) % 26;
                    encryptedChar = (char)(asciiCH + (int)'a');
                }
                else
                {
                    if (char.IsUpper(ch))
                    {
                        asciiCH = ((int)ch - (int)'A' + shift) % 26;
                        encryptedChar = (char)(asciiCH + (int)'A');
                    }
                    else
                    {
                        encryptedChar = ch;
                    }
                }
                encryptedString.Append(encryptedChar.ToString());
            }
            return encryptedString.ToString();
        }
    }
}

#include <stdio.h>

void encrypt_decrypt_String(int kShift, int pOption);

int main()
{
	int option = 0;
	int shift = 0;
	printf("Enter the shift for caeser cipher..\n");
	scanf("%d",&shift);
	printf("Enter 1 to encrypt and 0 to decrypt..\n");
	scanf("%d",&option);
	while(getchar() != '\n');
	encrypt_decrypt_String(shift, option);
}

void encrypt_decrypt_String(int kShift, int pOption)
{
	char ch;
	ch = getchar();
	while(ch != '\n')
	{
		if(ch == ' ')
		{
			putchar(' ');
		}
		else
		{
			if(pOption == 1)
				putchar(ch + kShift);
			else if(pOption == 0)
				putchar(ch - kShift);
			else
			{
				printf("Option not supported..\n");
				break;
			}
		}
		ch = getchar();
	}
	putchar(ch);
}

void ceaser ( char* string )
{
While ( *string ! = NULL )
{ int offset = *string – ‘A’ ;
if( offset < 24 ) *string = *string + 3
else /* *string is X,Y,Z */
{
*string = ‘A’ + ( (offset + 3) % 26 ) – 1
}
}