Compilare: user.cpp: In function ‘int main()’: user.cpp:66: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:67: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:68: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:72: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:73: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result user.cpp: In function ‘long long int calc(int, int)’: user.cpp:28: warning: ‘nl’ may be used uninitialized in this function /tmp/ccuiev5N.o: In function `main': user.cpp:(.text+0x2f6): warning: the `gets' function is dangerous and should not be used.