What this lines in bubble sort algorithm means?

In Introduction to programming with C++ 6th edition book, it explain the bubble sort algorithm with C++ and i understand it, but there is two lines of code I'm not understand why they in the code, when I tried to understand code I erase them and nothing changed and the algorithm still working. So I still confused about them. there is the code;

int main()
 {
     int numbers[4] = {23, 46, 12, 35};
     int sub = 0; //keeps track of subscripts
     int temp = 0; //variable used for swapping
     int maxSub = 3; //maximum subscript
     int lastSwap = 0; //position of last swap
     char swap = 'Y'; //indicates if a swap was made

     //repeat loop instructions as long as a swap was made
     while (swap == 'Y')
     {
     swap = 'N'; //assume no swaps are necessary

     sub = 0; //begin comparing with first
     //array element

     //compare adjacent array elements to determine
     //compare adjacent array elements to determine
     //whether a swap is necessary
     while (sub < maxSub)
     {
         if (numbers[sub] > numbers[sub + 1])
         {
             //a swap is necessary
             temp = numbers[sub];
             numbers[sub] = numbers[sub + 1];
             numbers[sub + 1] = temp;
             swap = 'Y';
             lastSwap = sub;
         } //end if
         sub += 1; //increment subscript
         } //end while

         maxSub = lastSwap; //reset maximum subscript
     } //end while

     //display sorted array
     for (int x = 0; x < 4; x += 1)
        cout << numbers[x] << endl;
     //end for

     system("pause");
     return 0;
 } //end of main function 

so I don't understand lastSwap = sub & maxSub = lastSwap. are they important or I'm right about erase them from the code? can anyone explain to it to me.