Question

Write a program in c++, 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

Strings Will be used to test code!

Some suggestions (NOT requirements):

1. C++ string library functions would be useful here
2. You can process the C++ string one char at a time if you use the length member function

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.

Main

-user input processing -repeat if wanted

   -clean up of dynamic storage (delete)

|

_____________________________ |____________________________

   | | |

Input encrypt/decrypt output

-read string -read from dynamic storage -get results

-put into dynamic storage -encrypt/decrypt -output results

   -store in dynamic storage

Answer 1

C++ Program:

/* C++ Program that decrypts the given cipher text by left rotating by 13 */

#include <iostream>
#include <cstring>
#include <stdlib.h>

using namespace std;

//Function prototype
char* decrypt(char*);
char* encrypt(char*);
char* inputString();

//Main function
int main()
{
int opt;
char *str, *opstr;

while(1)
{
//Printing menu
cout << "\n\n ***** MENU ***** \n 1-Encryption \n 2-Decryption \n 3-Exit \n\n Your option: ";
cin >> opt;

if(opt == 1)
{
//Reading string
str = inputString();
opstr = encrypt(str);
cout << "\n Encrypted: " << opstr;
delete[] str;
}
else if(opt == 2)
{
//Reading string
str = inputString();
opstr = decrypt(str);
cout << "\n Decrypted: " << opstr;
delete[] str;
}
else
{
return 0;
}
}

return 0;
}

//Function that reads the string
char* inputString()
{
char *str;

//Allocating memory
str = new char[25];

cin.ignore();

cout << "\n Enter String: ";
cin.getline(str, 100);

return str;
}

//Function that decodes given message using left rotational shift key
char* decrypt(char* cipher)
{
int i,j;

//Shift value 13
int val, shift=13;

//Character array
char *decodedMesg = new char[25];

//Looping over each character
for(i=0; i<strlen(cipher); i++)
{
//Getting Ascii values
val = (int)(cipher[i]);

//For Upper case letters
if(val >= 65 && val <= 90)
{
//Boundary crossing condition
if( (val - shift) < 65 )
val = 90 - abs(( (val - shift) - 65 )) + 1;
else
val = val - shift;

//Decrypting
decodedMesg[i] = (char)(val);
}
//For Lower case letters
else if(val >= 97 && val <= 122)
{
//Lower case
if( (val - shift) < 97 )
val = 122 - abs(( (val - shift) - 97 )) + 1;
else
val = val - shift;

//Decrypting
decodedMesg[i] = (char)(val);
}
//Other than letters
else
decodedMesg[i] = cipher[i];
}

//Adding string termination character
decodedMesg[i] = '\0';

//Returning the plain text
return decodedMesg;
}

//Function that decodes given message using left rotational shift key
char* encrypt(char* plain)
{
int i,j;

//Shift value 13
int val, shift=13;

//Character array
char *decodedMesg = new char[25];

//Looping over each character
for(i=0; i<strlen(plain); i++)
{
//Getting Ascii values
val = (int)(plain[i]);

//For Upper case letters
if(val >= 65 && val <= 90)
{
//Boundary crossing condition
if( (val + shift) > 90 )
val = 65 + abs(( 90 - (val + shift) )) - 1;
else
val = val + shift;

//Decrypting
decodedMesg[i] = (char)(val);
}
//For Lower case letters
else if(val >= 97 && val <= 122)
{
//Lower case
if( (val + shift) > 122 )
val = 97 + abs(( 122 - (val + shift) )) - 1;
else
val = val + shift;

//Decrypting
decodedMesg[i] = (char)(val);
}
//Other than letters
else
decodedMesg[i] = plain[i];
}

//Adding string termination character
decodedMesg[i] = '\0';

//Returning the plain text
return decodedMesg;
}
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Sample Run: