A simple ROT13 encryption program for you to critique.

ROT13.cpp

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
#include <stdlib.h>
 
std::string getfile(int x);
std::string outputfile(std::string a);
std::string crypt(std::string a);
 
int main(int argc, char const *argv[])
{
    std::string input = "", output = "", pause = "";
        int x=0;
 
        input = getfile(x); //Input = user entered file name
        
        if(input == "")         //Check if input is empty
        {
                std::cout << "Invalid text, exiting program.";
                std::cin;
                return 0;
        }
        output = crypt(input);          //crypt input information
        if(output == "")                        //Check if encrypted text is empty
        {
                std::cout << "Problem encrypting text, closing.";
                std::cin;
                return 0;
        }
        else
                outputfile(output);
 
        std::cout << "\nEnter any text to close the program.\n";
        std::cin >> pause;
        return 0;
}
 
std::string getfile(int x)
{
        std::string orig="", again="";  //string declarations
        std::cout << "Please enter an existing filename (Example.txt): ";
        std::cin >> orig;                               //input file name
                
        std::fstream input;                             //file stream
        input.open(orig.c_str());               //open input file name
        if(input.is_open())                                                             // Check if file is open
                std::cout << "File opened succesfully.\n";
        else
        {
                std::cout << "File cannot be opened, would you like to try again?(Y/N)\n";
                std::cin >> again;                      // Ask to enter another file name if first failed
                if(again == "y")
                {
                        getfile(x);
                        exit;
                }
                else
                        exit;
        }
 
        std::getline(input, orig);
        std::cout << "\nOriginal text reads:\n" << orig << "\n\n";
        input.close();                                  // Close file stream
        return orig;                                    // Return file name
}
 
std::string outputfile(std::string a)
{
                std::string ret="";
                std::fstream output;
                output.open("Crypted.txt", std::fstream::out);  //Open file with title "Crypted.txt"
                if(output.is_open())                            //Check if file was opened
                        std::cout << "Output file opened succesfully with the filename \"Crypted.txt\"\n";
                else
                {
                        std::cout << "Output file not opened succesfully, exiting the program.\n";
                        std::cin >> ret; 
                }
                output << a;                                    //Output encrypted string to "Crypted.txt"
                output.close();                                 //Close output file stream
                return a;
}
 
std::string crypt(std::string a)
{
        int z = a.length(), i=0;                
        for(i=0; i<=(z); i++)                                   //Rot13 Algorithm
        {
                if(a[i] < 91 && a[i] > 64)              //uppercase
                {
                        if(a[i] < 78)
                                a[i] = a[i] + 13;
                        else
                        a[i] = a[i] - 13;
                }
                if(a[i] < 123 && a[i] > 96)     //lowercase
                {
                        if(a[i] < 110)
                                a[i] = a[i] + 13;
                        else
                                a[i] = a[i] - 13;
                }
        }
        return a;                                                               //return encrypted string
}