Compilare: user.cpp: In function ‘int main()’: user.cpp:24:18: warning: array subscript has type ‘char’ [-Wchar-subscripts] u1[ a[i] ]++; ^ user.cpp:26:18: warning: array subscript has type ‘char’ [-Wchar-subscripts] u2[ b[i] ]++; ^ user.cpp:14:35: 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:15:37: 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:20:16: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(a + 1); gets(b + 1); ^ user.cpp:20:29: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(a + 1); gets(b + 1); ^ /tmp/ccHztgio.o: In function `main': user.cpp:(.text.startup+0x56): warning: the `gets' function is dangerous and should not be used.