prog.cpp:6:10: error: initializer specified for non-virtual method 'char AbstractFile::read_at_offset(int)'
char read_at_offset(int _n) = 0;
^
prog.cpp: In function 'int main()':
prog.cpp:20:5: error: 'k' was not declared in this scope
k = 4;
^
prog.cpp:21:14: error: return-statement with no value, in function returning 'int' [-fpermissive]
if (k%2) return;
^
prog.cpp:32:23: error: '_opened' was not declared in this scope
assess(s, _opened);
^
prog.cpp:45:15: error: '_opened' was not declared in this scope
--_opened;
^
prog.cpp:47:15: error: '_opened' was not declared in this scope
++_opened;
^
prog.cpp:50:47: error: '_opened' was not declared in this scope
assess(file->read_at_offset(first+k), _opened);
^