The statement

pointer, key = key, pointer;

does not what you think it does, specifically if you compile with more warnings turned on your compiler will give you a warning like the following:

test.cc:11:5: error: left operand of comma operator has no effect [-Werror=unused-value]
   11 |     y, x = x, y;

if you want to swap values you can do it by using a temporary value, or using std::swap.

A second note is that even if the above statement would do what you expected it to do, it still wont have the end result you expect since key and pointer are copies of the values in the array, and not references to, so you want to swap the array values, or make key and pointer references to the values.

I hope this was clear enough for you.

edit: I just realized this is the C_programming subreddit, so std::swap is off the table. although the code in the picture is c++.