foo.cc: In function 'int main()':
foo.cc:49:19: warning: 'year2' may be used uninitialized in this function [-Wmaybe-uninitialized]
   sum=sum+MonthDay(year,m);
           ~~~~~~~~^~~~~~~~
foo.cc:11:6: note: 'year2' was declared here
  int year2,month2,day2; 
      ^~~~~
foo.cc:49:19: warning: 'year1' may be used uninitialized in this function [-Wmaybe-uninitialized]
   sum=sum+MonthDay(year,m);
           ~~~~~~~~^~~~~~~~
foo.cc:10:6: note: 'year1' was declared here
  int year1,month1,day1; 
      ^~~~~