Compilare: user.cpp: In function ‘bool validate(std::vector<int>)’: user.cpp:9:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) { ^ user.cpp:10:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = i+1; j < a.size(); j++) { ^ user.cpp: In function ‘int main()’: user.cpp:37:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < v.size(); i++) { ^