/in/foo.cc: In function 'int main()':
/in/foo.cc:13:14: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]
  if(!sign) v=-v;
              ^~
/in/foo.cc:52:11: note: 'b' was declared here
   int k,a,b; read(k),read(a),read(b);
           ^
/in/foo.cc:13:14: warning: 'a' may be used uninitialized in this function [-Wmaybe-uninitialized]
  if(!sign) v=-v;
              ^~
/in/foo.cc:52:9: note: 'a' was declared here
   int k,a,b; read(k),read(a),read(b);
         ^
/in/foo.cc:13:14: warning: 'k' may be used uninitialized in this function [-Wmaybe-uninitialized]
  if(!sign) v=-v;
              ^~
/in/foo.cc:52:7: note: 'k' was declared here
   int k,a,b; read(k),read(a),read(b);
       ^