C++ :: Read (three Digit) Integer Representing Value To Be Encrypted

I have been working on some C++ code that doesn't seem to be going right. I'm wanting it to read a (three-digit) integer representing the value to be encrypted, a (one-digit) integer representing the encryption key, encrypt the value and print the encrypted value. The encrypting method used is that each digit in the given number is replaced by ((the sum of that digit plus key) modulo 10) then the first and last “encrypted” digits are swapped.

For example, if the number entered was 216 and the key given was 7, after applying the encryption procedure described the first digit (2) would become 9, the middle digit (1) would become 8 and the last digit (6) would become 3. The first and last encrypted digits are then swapped. The program displays the encrypted number: that is 389 in this case.

#include <iostream>
using namespace std;
int main() {
int isolateDigits();
int replaceDigits();
int swapDigit1withDigit3();

[Code] ....