Compilare: user.cpp: In function ‘std::vector<std::vector<unsigned int> > process_dragons(std::vector<Point>)’: user.cpp:52:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if( 0 <= next_cell.x && next_cell.x < n && ^ user.cpp:53:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] 0 <= next_cell.y && next_cell.y < m ) { ^ user.cpp:54:80: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(!visited[next_cell.x][next_cell.y] && map[next_cell.x][next_cell.y] != -1) { ^ user.cpp: In function ‘int main()’: user.cpp:80:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < n; ++i) { ^ user.cpp:81:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < m; ++j) { ^