sudoku.cpp: In function 'int main()': sudoku.cpp:40: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result sudoku.cpp:41: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result sudoku.cpp:47: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result