The Caesar Cipher - C++ console

/***********************************************************************************
/ Name: Brian Butler
/ Class: 9:00am - 10:45 
/ Professor: Gary Hartell
/ Date Finished: Nov 5, 2011
/
/ Assignment:Caesar Cipher
/
/					   					 Descripion:
/		This program uses the shift method of encryption - known as the Caesar Cipher
/
/
************************************************************************************/

#include <iostream>
#include <string>
#include <conio.h>
#include <sstream>
#include <algorithm>
using namespace std;

/********************************  FUNCTION PROTOTYPES  ******************************/
char encrypt(char c, int key);
char decrypt (char c, int key);
void menu();
void choice(int pick);
void manipulateString();
void outputEncryption();
void outputDecryption();
void harderToCrack(string &str);

/**********************************  GLOBAL VARIABLES  *******************************/
string inputString;
int key, size;
char chars[1000];

/********************************      MAIN METHOD      ******************************/
int main()
{
    cout << "Please enter a sentence to encrypt or decrypt:" << endl;

    getline(cin, inputString);// user sentence input

    size=inputString.size();// number of characters in the user's sentence

    endl(cout);

    do//get the shift key
    {
        cout << "Please enter an integer between -25 and 25 for the shift key: ";

        cin >> key;
    }
    while(key < -25 || key > 25);

    endl(cout);

    menu();/* call the menu function                                                 */

    endl (cout);
    endl (cout);
    cout << "Please press any key to EXIT!" << endl;
    getch();

    return 0;
}// END MAIN

/*******************************  Menu Function **************************************/
void menu()
{
    int x;
    cout << "Please choose a number from the following menu:" << endl;
    endl(cout);
    cout << "1. Encrypt my sentence." << endl;
    cout << "2. Encrypt and remove all white spaces\n"
         << "           and make it all lower case." << endl;
    cout << "3. Decrypt my sentence." << endl;

    cin >> x;
    choice(x);// call choice function
}//end menu function

/************************** Manipulate String Function *******************************/
void manipulateString()
{
        int size=inputString.size();

        for (int a=0;a<=size;a++)
        {
            chars[a]=inputString[a];/** convert the string into a character array*/
        }
}//end manipulateString function

/************************** Output Encryption Function *******************************/
void outputEncryption()
{
        cout << "\nEncrypted: " ;

        for(int i = 0; i < size; i++)
        {
            char c = chars[i];
            char encrypted = encrypt(c, key);

            cout << encrypted;
        }
}//end outputEncryption function

/************************** Output Decryption Function *******************************/
void outputDecryption()
{
       cout << "\nDecrypted: ";

        for(int i = 0; i < size; i++)
        {
            char c = chars[i];
            char decrypted = decrypt(c, key);

            cout << decrypted;
        }
}//end outputDecryption function

/*******************************  Choice Function  ***********************************/
void choice(int pick)
{
    if (pick ==1)
    {
        manipulateString();
        outputEncryption();
    }
    else if (pick ==2)
    {

         harderToCrack(inputString);
         manipulateString();
         outputEncryption();
    }
    else if (pick ==3)
    {
         manipulateString();
         outputDecryption();
    }
    else
    {
        cout << "I'm sorry, that is not a valid choice." << endl;
    }
}//end choice function

/******************************* Encryption Function *********************************/
char encrypt(char c, int key)
{
    char alphabet[26];
    int i = 0;

    for(char ch = 'a'; ch <= 'z'; ++ch)/* fills alphabet array with the alphabet     */
    {
        alphabet[ch-'a']=ch;
    }

/*                          BELOW while loop FROM:
	             http://www.cs.utsa.edu/~wagner/laws/Acaesar.html                    */

      			while (i < 26)
                {
         			 if (c == alphabet[i])
                     return alphabet[(i + key + 26)%26];
            		 i++;
      			}
                return c;
}//end encryption function

/******************************* Decryption Function *********************************/
char decrypt (char c, int key)
{
    char alphabet[26];
    int i = 0;

    for(char ch = 'a'; ch <= 'z'; ++ch)/* fills alphabet array with the alphabet     */
    {
        alphabet[ch-'a']=ch;
    }

/*                               BELOW while loop FROM:
	             http://www.cs.utsa.edu/~wagner/laws/Acaesar.html                    */

      			while (i < 26)
                {
         			 if (c == alphabet[i])
                     return alphabet[(i - key + 26)%26];
            		 i++;
      			}
                return c;
}//end decryption function

/******************************* harderToCrack Function ******************************/
void harderToCrack(string &str)//must use a reference variable here
{
    for (int i = 0; i < size; i++)/* this for loop removes all white spaces,         */
    {
        if (str[i] == ' '|| str[i] == '.' || str[i] =='?')
        {
            str.erase(i,1);
            i--;
        }
    }

    for(int y = 0; y < size; y++)/* this for loop makes everything lower case        */
    {
		str[y] = tolower(str[y]);
    }

}//end harderToCrack function

//END OF CODE