/in/foo.cc: In function 'int main()':
/in/foo.cc:33:19: warning: 'len' may be used uninitialized in this function [-Wmaybe-uninitialized]
         a.data[len] ? a.data[0] = len : a.data[0] = --len;
         ~~~~~~~~~~^
/in/foo.cc:26:13: note: 'len' was declared here
         int len;
             ^~~