foo.cc: In function 'int main()':
foo.cc:13:6: warning: operation on 'sum' may be undefined [-Wsequence-point]
   sum=sum=MonthDay(year,m);
   ~~~^~~~~~~~~~~~~~~~~~~~~
foo.cc: In function 'int MonthDay(int, int)':
foo.cc:33:2: warning: this 'else' clause does not guard... [-Wmisleading-indentation]
  else
  ^~~~
foo.cc:36:3: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'else'
   return day;
   ^~~~~~