Compilare: user.cpp: In function ‘int main()’: user.cpp:32:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("swap.in","r",stdin); ^ user.cpp:33:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("swap.out","w",stdout); ^ user.cpp:35:12: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(a); gets(b); n = strlen(a); m = strlen(b); ^ user.cpp:35:21: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(a); gets(b); n = strlen(a); m = strlen(b); ^ /tmp/cc8LYJuY.o: In function `main': user.cpp:(.text.startup+0x56): warning: the `gets' function is dangerous and should not be used.