foo.cc:10:11: error: 'int clock' redeclared as different kind of symbol
 int n, m, clock;
           ^~~~~
In file included from /usr/include/pthread.h:24:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/gthr-default.h:35,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/gthr.h:148,
                 from /usr/include/c++/6/ext/atomicity.h:35,
                 from /usr/include/c++/6/bits/ios_base.h:39,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from foo.cc:3:
/usr/include/time.h:189:16: note: previous declaration 'clock_t clock()'
 extern clock_t clock (void) __THROW;
                ^~~~~
foo.cc: In function 'void fun()':
foo.cc:20:23: warning: ISO C++ forbids decrementing a pointer of type 'clock_t (*)() throw () {aka long int (*)() throw ()}' [-Wpointer-arith]
   out[current] = clock--;
                       ^~
foo.cc:20:23: error: lvalue required as decrement operand
foo.cc:21:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0; i<edge[current].size(); i++){
                ~^~~~~~~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:33:10: error: assignment of function 'clock_t clock()'
  clock = n;
          ^
foo.cc:33:10: error: cannot convert 'int' to 'clock_t() throw () {aka long int() throw ()}' in assignment