Compilare: user.cpp: In function ‘int main()’: user.cpp:48:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<strlen(b); ++i) ^ user.cpp:44:33: 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:45:35: 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:46:12: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(a); ^ user.cpp:47:12: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(b); ^ /tmp/cc6yQGy6.o: In function `main': user.cpp:(.text.startup+0x58): warning: the `gets' function is dangerous and should not be used.