foo.cc: In function 'int main()':
foo.cc:9:18: warning: unused variable 'm1' [-Wunused-variable]
  int yy, mm, dd, m1, thatgodays, less=10000, j, k;
                  ^~
foo.cc: In function 'int isleap(int)':
foo.cc:33:28: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  return x%4==0 || x%100==0 && x%400==0;
                   ~~~~~~~~~^~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:13:12: warning: 'thatgodays' may be used uninitialized in this function [-Wmaybe-uninitialized]
  thatgodays=thatgodays+dd;
  ~~~~~~~~~~^~~~~~~~~~~~~~