foo.cc: In function ‘bool isrn(int)’:
foo.cc:8:1: warning: control reaches end of non-void function [-Wreturn-type]
    8 | }
      | ^
foo.cc: In function ‘int main()’:
foo.cc:43:11: warning: ‘ans’ may be used uninitialized [-Wmaybe-uninitialized]
   43 |     cout<<ans;
      |           ^~~
foo.cc:11:24: note: ‘ans’ was declared here
   11 |     int year,month,day,ans;
      |                        ^~~