/in/foo.cc: In function 'int main()':
/in/foo.cc:144:8: warning: unused variable 'opt' [-Wunused-variable]
   char opt[10];
        ^~~
/in/foo.cc:155:23: warning: 'w' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if(x0 == 1) a[y0] = w;
                 ~~~~~~^~~