Compilare: user.cpp: In function ‘int main()’: user.cpp:17:43: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("twosets.in" , "r" , stdin ) ; ^ user.cpp:18:45: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("twosets.out" , "w" , stdout ) ; ^ user.cpp:19:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d" , &t ) ; ^ user.cpp:23:19: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets( s ) ; ^ user.cpp:48:20: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets( s1 ) ; ^ /tmp/ccMG3FJA.o: In function `main': user.cpp:(.text.startup+0x94): warning: the `gets' function is dangerous and should not be used.