Compilare: user.cpp: In function ‘int main()’: user.cpp:57:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < Plus.size() && j < Minus.size()) ^ user.cpp:57:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < Plus.size() && j < Minus.size()) ^ user.cpp:66:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; i < Plus.size(); ++i) ^ user.cpp:68:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; j < Minus.size(); ++j) ^