help i can not figure this out.

my home is to encryption a four digit number

I have to add 7 and use mod 10-- i think i have that part but now i need to swap the first number with the third and second with the fourth. i can not get it--here is my code

i know 41 is wrong but i am drawing a blank

//christine gershen

// Exercise 4.17: Encryption.cpp

// Encrypts data given by user.

#include <iostream> // required to perform C++ stream I/O

#include <iomanip> // required to perform setprecision stream manipulator

using namespace std; // for accessing C++ Standard Library members

int main() // function main begins program execution

{

int main=0;

int digit_one; //store digit one

int digit_two; //store digit two

int digit_three; //store digit three

int digit_four; //store digit four

int encryption; //store encryption

cout <<"Enter four-digit number:"; //asking the user to enter four-digit number

cin >> main; //four-digit number

digit_one=main/1000%10; // digit_one is first four-digit number

digit_two=main/100%10; // digit_two is second four-digit number

digit_three=main/10%10; //digit_three is third four-digit number

digit_four=main%10; //digit_four is fourth four-digit number

digit_one+=7%10; //add digit_two to 7 and mod 10

digit_two+=7%10; //add digit_two to 7 and mod 10

digit_three+=7%10; //add digit_three to 7 and mod 10

digit_four+=7%10); //add digit_four to 7 and mod 10

encryption=digit_three digit_four digit_one digit_two

cout <<"Encrypted digits:" << encryption <<endl; // display encrypted numbers

return 0; // indicate that program ended successfully

}// end function main

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