foo.c: In function ‘main’:
foo.c:17:13: warning: unused variable ‘right’ [-Wunused-variable]
   17 |         int right = strlen(n) - 1;
      |             ^~~~~
foo.c:16:13: warning: unused variable ‘left’ [-Wunused-variable]
   16 |         int left = 0;
      |             ^~~~