#include <iostream>
#include <string>
using namespace std;
char caesar(char);
int main()
{
    string input;
    do
        {
            cout << "Enter cipertext and press enter to continue." << endl;
            cout << "Enter blank line to quit." << endl;
            getline(cin, input);
            string output = "";
            for (int x = 0; x < input.length(); x++)
                {
                    output += caesar(input[x]);
                }
            cout << output << endl;
        }
    while (!input.length() == 0);
} //end main

char caesar(char c)
{
    if (isalpha(c))
        {
            c = toupper(c); //use upper to keep from having to use two seperate for A..Z a..z
            c = (((c - 65) + 13) % 26) + 65;
        }
    //if c isn't alpha, just send it back.
    return c;
}

/*
Enter cipertext and press enter to continue.
Enter blank line to quit.
Sanfoundry
FNASBHAQEL
Enter cipertext and press enter to continue.
Enter blank line to quit.