debugger edits process memory

me@oliphant:~$ cat lala.cpp
#include <iostream>
#include <unistd.h>>

int main(int argc, char** argv) {
    volatile int i(0);

    while(true){
        std::cout << i << std::endl;
        sleep(5);
    }
}
me@oliphant:~$ g++ -ggdb lala.cpp
me@oliphant:~$ ./a.out & gdb a.out $! -f a.out
[1] 98933
0
Excess command line arguments ignored. (a.out)
GNU gdb 6.3.50-20050815 (Apple version gdb-1461.2) (Fri Mar  5 04:43:10 UTC 2010)
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "x86_64-apple-darwin"...Reading symbols for shared libraries ... done

/Users/me/98933: No such file or directory
Attaching to program: `/Users/me/a.out', process 98933.
Reading symbols for shared libraries ++. done
0x00007fff888b3a6a in __semwait_signal ()
(gdb) break lala.cpp:9
Breakpoint 1 at 0x100000d4b: file lala.cpp, line 9.
(gdb) c
Continuing.
0

Breakpoint 1, main (argc=1, argv=0x7fff5fbfef28) at lala.cpp:9
/Users/me/lala.cpp:9:154:beg:0x100000d4b
(gdb) print i=22
$1 = 22
(gdb) c
Continuing.
22

Breakpoint 1, main (argc=1, argv=0x7fff5fbfef28) at lala.cpp:9
/Users/me/lala.cpp:9:154:beg:0x100000d4b
(gdb) The program is running.  Quit anyway (and detach it)? (y or n) y
Detaching from program: `/Users/me/a.out', process 98933.
me@oliphant:~$ 22
fg
./a.out
22
^C
me@oliphant:~$