Compilare: user.cpp: In function ‘int main()’: user.cpp:88:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( i = 0; i < C1.size(); i++ ) ^ user.cpp:90:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( i = 0; i < C2.size(); i++ ) ^ user.cpp:92:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( i = 0; i < C3.size(); i++ ) ^ user.cpp:94:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( i = 0; i < C4.size(); i++ ) ^