Compilare: user.cpp: In function ‘int main()’: user.cpp:98:11: warning: statement has no effect [-Wunused-value] for (j; j < op.size(); j++) ^ user.cpp:98:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j; j < op.size(); j++) ^ user.cpp:104:19: warning: statement has no effect [-Wunused-value] for (i; i <= l; i++) ^