Compilare: user.cpp: In function ‘void write()’: user.cpp:39:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < my_vector.size(); ++i) ^ user.cpp: In function ‘void start_backtracking()’: user.cpp:50:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < immortals.size(); ++i) { ^