Question

Can someone please help me for this assignment?

Cryptography — the science of secret writing — is an old science; the first recorded use was well before

1900 B.C. An Egyptian writer used previously unknown hieroglyphs in an inscription.

We will use a simple substitution cypher called rot13 to encode and decode our secret messages.

ROT13 ("rotate by 13 places", sometimes hyphenated ROT-13) is a simple letter substitution cipher that replaces a letter with the 13th letter after it, in the alphabet. ROT13 is a special case of the Caesar cipher which was developed in ancient Rome.

Decryption Key

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

(letter above equals below, and vice versa)

As you can see, A becomes N, B becomes O and so on.

Your job is to write a program, with at least four functions, including main, which must do the following:

1. Ask user whether they want to encode or decode a message - if no, then terminate

2. Take the input string from the user, store it in dynamic memory (use new)

3. As appropriate, encode or decode the message using Rot13.

4. Output the encoded/decoded message

5. Delete the input string from dynamic memory (use delete)

Input will be a string of no more than 25 characters.

Blanks get replaced with blanks.

Do not worry about punctuation; there will be no punctuation in the string.

ALPHABET becomes NYCUNORG

Test your program with the following strings:

TAF VF

paddrpf

I'll be using other strings to test your code.

Answer 1

#include <iostream>
#include <cctype>

using namespace std;

int main()
{
//declaring required variable
char choice;
//loop for iterative encryption/decryption
   do
   {
   //asking for choice
   cout<<"Do you want to encrypt/decrypt a string? (y or n) :";
   cin>>choice;
   //if user want to encrypt or decrypt
   if(choice=='y')
   {
   //declaring output variable
   string result="";
   cout<<"Enter a string ::";
   //creating dynamic memory
   string *input = new string();
   //reading input to the dynamic memory
//this will remove the nw line character present in the input buffer
getline(cin,*input);
//this will read the input from the user
getline(cin,*input);
   //iterating through the string to encrypt/decrypt each character
   for(int i=0;i<(*input).length();i++)
   {
   //converting the character to upper case
   char temp=toupper((*input)[i]);
   //checking if the character is alphabet or not
   if(isalpha(temp))
   {
   //rotating the character by 13 places
   //the %26 is there to ensure the ascii value do not exceed the value of 'Z'
   int new_character=65+(((int)temp-65)+13)%26;
   //adding new character to the output string
   result = result + (char)new_character;
   //end of if
   }
   //if the character is not a alphabet
   else
   {
   //adding the charater to the output string
   result = result + temp;
   //end of else
   }
   //end of for
   }
   //deleting the input stored in dynamic memory
   delete input;
   //printing the encrypted or decrypted string
   cout<<"Resultant String::"<<result;
   }
   //end of while
   }while(choice!='n');
   //end of function
}