Compilare: user.cpp: In function ‘void sort2()’: user.cpp:20:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1; i<a.length(); i++) ^ user.cpp: In function ‘void read()’: user.cpp:13:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &v); ^ user.cpp: In function ‘int main()’: user.cpp:41:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("charlie.in", "r", stdin); ^ user.cpp:42:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("charlie.out", "w", stdout); ^