Compilare: user.cpp: In function ‘void _1()’: user.cpp:22:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); ++i) ^ user.cpp: In function ‘void _2()’: user.cpp:50:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); ++i) ^ user.cpp:60:11: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if(x == mix/* && (ch.empty() || ch[ch.size()-1] != 'U')*/) ^