foo.cc: In function 'int month(int, int)':
foo.cc:10:19: error: 'year' was not declared in this scope
   10 |     if (m == 2 && year(y))
      |                   ^~~~
foo.cc: In function 'int main()':
foo.cc:57:18: error: 'm2' was not declared in this scope; did you mean 'd2'?
   57 |     cin >> y2 >> m2 >> d2;
      |                  ^~
      |                  d2
foo.cc:55:13: warning: unused variable 'mo2' [-Wunused-variable]
   55 |     int y2, mo2, d2;
      |             ^~~

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