foo.cc: In function 'int main()':
foo.cc:23:13: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
   23 |    for (; s != NULL; s = s->next);
      |             ^
foo.cc:61:5: note: 's' was declared here
   61 |  su s(n);
      |     ^

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