foo.cc: In function 'int main()':
foo.cc:50:19: warning: 'y2' may be used uninitialized in this function [-Wmaybe-uninitialized]
   sum=sum+MonthDay(year,m);
           ~~~~~~~~^~~~~~~~
foo.cc:11:6: note: 'y2' was declared here
  int y2,m2,d2; 
      ^~
foo.cc:10:6: warning: 'y1' may be used uninitialized in this function [-Wmaybe-uninitialized]
  int y1,m1,d1; 
      ^~