Compilare: user.cpp: In function ‘void readdata()’: user.cpp:26: warning: unused variable ‘v2’ user.cpp:23: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:24: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:28: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp: In function ‘void df(int)’: user.cpp:41: warning: comparison between signed and unsigned integer expressions user.cpp:44: warning: comparison between signed and unsigned integer expressions user.cpp:51: warning: comparison between signed and unsigned integer expressions