C$++$ program

loops, conditionals, and functions

Data types, particularly char and int

Pass by reference parameters in C$++$

Buffered input and output $($cin and cout$)$

DO NOT USE arrays, vectors, strings, or any other data structure. The goal is to practice with the primitive data types and control structures in C$++.$

Sample Ciphers

Right shift of $3$:

Plain text: hello world

Encrypted: khoorczruog

Left shift of $5$:

Plain text: execute plan eagle at midnight

Encrypted: s ypo vkgwiv wbg vwovhdzidbco

Left shift of $3$:

Plain text: the quick brown fox jumps over the lazy dog

Encrypted: qebxnrf hxzoltkxcluxgrjmpxlsboxqebxiywvxald

Sample runs of the program

Upon running your program, the user should see the following:

Please select from the following options:

Encrypt $($e$)$

Decrypt $($d$)$

Quit $($q$)$

Choice:

This $$main menu$$ should be displayed after every operation, allowing for repeated encryption$/$decryptions$,$ until the user chooses to quit.

Invalid choice

Any selection other than these three should result in an error message, with the prompt repeating until a valid selection is made. For example $($user input is underlined in bold$)$:

Please select from the following options:

Encrypt $($e$)$

Decrypt $($d$)$

Quit $($q$)$

Choice: x

x is not a valid option, try again.

Please select from the following options:

Encrypt $($e$)$

Decrypt $($d$)$

Quit $($q$)$

Encrypt

If the user selects e$,$ the program should prompt the user for a shift value and direction and a message to encrypt. The encrypted message should then be displayed. For example:

Please select from the following options:

Encrypt $($e$)$

Decrypt $($d$)$

Quit $($q$)$

Choice: e

Enter the direction of the shift $($l$/$r$)$: l

Enter the shift number $($integer$)$: $3$

Enter the phrase to encrypt: cats and dogs

Result: yqpxykaxaldp

Please select from the following options:

Encrypt $($e$)$

Decrypt $($d$)$

Quit $($q$)$

Choice:

Decrypt

A lot like encrypt, but in reverse. Any phrases that you encrypt should be able to be decrypted back to the original message. For example:

Please select from the following options:

Encrypt $($e$)$

Decrypt $($d$)$

Quit $($q$)$

Choice: d

Enter the direction of the shift $($l$/$r$)$: l

Enter the shift number $($integer$)$: $3$

Enter the phrase to decrypt: yqpxykaxaldp

Result: cats and dogs

Please select from the following options:

Encrypt $($e$)$

Decrypt $($d$)$

Quit $($q$)$

Quit

If the user selects q$,$ the program should exit without further prompting.

encrypt.cpp:

$//$private functions

$//$ Define and use at least one useful private function

$//$ Public functions

$//$ Define and implement the functions declared in encrypt.h here.

encrypt.h:

$//$ Do not modify this header file.

#ifndef ENCRYPT$\_$H

#define ENCRYPT$\_$H

$//$ Process input according to the given parameters.

$//$ This function should read from cin and write to cout.

void process$($char mode, int shift, char dir$)$;

$//$ Encrypt a single character

$//$ Note that shift is negative for left, positive for right

char encrypt$($char c$,$ int shift$)$;

$//$ Decrypt a single character

$//$ Note that shift is negative for left, positive for right

char decrypt$($char c$,$ int shift$)$;

#endif $//$ ENCRYPT$\_$H

main.cpp:

#include

#include "encrypt.h$"$

using namespace std;

$//$ Function declarations

$//$ Define these functions after main

$//$ Display the main menu and return the selected option

char main$\_$menu$()$;

$//$ Prompt for and write to the desired shift and direction

void get$\_$opts$($int &shift, char &dir$)$;

int main$()\{$

$//$ Main program entry point.

$//$ This function should:

$//-$ Display the main menu and get the selected option

$//-$ If the user selects quit, exit the progam $($stop looping$)$

$//-$ If user selects encrypt or decrypt:

$//-$ Call get$\_$opts to get the shift options$|$

$//-$Prompt for the phrase to encrypt$/$decrypt

$//-$ Call process from the encrypt library

$//-$ After each operation, display the main menu