Need some help with this program

So, I am required to make something that adds and substracts two 16 digit numbers, each of them composed of two 8 digit numbers respectively.
This needs to be done using integers only and using only If, switch or for.

what I have till now is this

Code:

#include <iostream>
#include <iomanip>
using namespace std;
int main()

{

  int number1l, number1r, number2l, number2r;
  int suml, sumr, diffl, diffr;
  char ope;


  cout << "number 1:";
  cin >> number1l >> number1r;

  cout << "number 2:";
  cin >> number2l >>  number2r;

  suml = number1l + number2l;
  sumr = number2r + number2r;

  diffl = number1l - number2l;
  diffr = number2r - number2r;

  if (sumr > 99999999)
    suml++;

 else if (diffr < 99999999)
    {  diffl--;
  diffr+=10000000;
    }
    
  cout << setfill('0');
  cout << "sum:"  << setw(8) <<  suml << setw(8) << sumr;
  cout << "diff" <<  setw(8) <<  diffl << setw(8) << diffr;

  return 0;
}

It all goes fine but somehow in the end I end up getting wrong calculations.

If i put 11111111 11111111 and 22222222 22222222
i get 3333333344444444 as sum and 1111111210000000 as difference.
What am i doing wrong here, any help would be appreciated.

Edit: Nevermind, found out what was wrong :/

If you look carefully you aren't actually adding the right things.

number1r adds number2r, number1l adds number2l.

This finds the right sum for the specific problem you mention, though I don't know what you would do for a carry.
The same mistake is repeated for minus.