Compilare: user.cpp: In function ‘void read()’: user.cpp:31:26: warning: array subscript has type ‘char’ [-Wchar-subscripts] x[++nx] = ax[ b[i] ][0]; ^ user.cpp:32:14: warning: array subscript has type ‘char’ [-Wchar-subscripts] ax[b[i]].pop_front(); ^ user.cpp: In function ‘void solve()’: user.cpp:49:10: warning: unused variable ‘j’ [-Wunused-variable] int i, j; ^ user.cpp: In function ‘int main()’: user.cpp:66:16: warning: array subscript has type ‘char’ [-Wchar-subscripts] ++u1[ a[i] ], ^ user.cpp:67:16: warning: array subscript has type ‘char’ [-Wchar-subscripts] ++u2[ b[i] ]; ^ user.cpp: In function ‘void read()’: user.cpp:19:31: 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:20:10: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(a); ^ user.cpp:25:10: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(b); ^ user.cpp: In function ‘int main()’: user.cpp:62:33: 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); ^ /tmp/ccBs0JxU.o: In function `read()': user.cpp:(.text+0x124): warning: the `gets' function is dangerous and should not be used.