Compilare: user.cpp: In function ‘void read()’: user.cpp:21: warning: unused variable ‘j’ 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:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp: In function ‘void df(int)’: user.cpp:54: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘int main()’: user.cpp:77: warning: comparison between signed and unsigned integer expressions user.cpp:82: warning: comparison between signed and unsigned integer expressions