Compilare: user.cpp: In function ‘int Find(int)’: user.cpp:16:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(; step < position[x].size() - 1; step <<= 1); ^ user.cpp:20:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if((i + step < position[x].size()) && (position[x][i + step] <= top) && (s[position[x][i + step]] == x)) ^ user.cpp: In function ‘int main()’: user.cpp:31:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("undo2.in", "r", stdin); ^ user.cpp:32:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("undo2.out", "w", stdout); ^ user.cpp:34:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &N); ^ user.cpp:38:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &Q, &x); ^