xy.cpp: In function 'int main()': xy.cpp:4: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result xy.cpp:5: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result xy.cpp:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result xy.cpp:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result xy.cpp:6: warning: 'nr' may be used uninitialized in this function