#include <iostream>
#include <cstdio>
#include <cstring>
#include <cctype>

using namespace std;

const int alphabet = 26;

int shift(int&);
void encryption(int&, char[alphabet], char [30]);
void decryption(int&, char[alphabet], char [30]);

int main()
{
    char value;
    char letters[alphabet] = {'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'};
    char input[30];
    int shiftamount;

    cout << "Which action do you want to perform?" << endl;
    cout << "(1) Encryption" << endl;
    cout << "(2) Decryption" << endl;

    while(value != 1 && value != 2)
    {
        cin >> value;

        switch(value)
        {
            case'1':
            {
                shift(shiftamount);
                encryption(shiftamount, letters, input);
            }

            case'2':
            {
                shift(shiftamount);
                decryption(shiftamount, letters,input);
            }
            default:
                cout << "Error: Wrong value chosen. Try again." << endl;
        }
    }

    return 0;
}

int shift(int& shiftamount)
{
    cout << "How many letters to the right do you want the alphabet to shift?" << endl;
    cin >> shiftamount;

    return 0;
}

void encryption(int& shiftamount, char letters[], char input[])
{
    cout << "Input the message you wish to encrypt:" << endl;
    cin.getline(input, 30);

    char cipher[30];

    for(int i = 0; i < alphabet; i++)
    {
        letters[i] = toupper(letters[i]);
        int x = input[i] - 'A';
        cipher[i] = x + shiftamount;
        cout << cipher[i];
    }

    return;
}

void decryption(int& shiftamount, char letters[], char input[])
{
    cout << "Input the message you wish to decrypt:" << endl;
    cin.getline(input, 30);

    char cipher[30];

    for(int i = 0; i < alphabet; i++)
    {
        int x = input[i] - 'a';
        cipher[i] = x + shiftamount;
        cout << cipher[i];
    }

    return;
}