Compilare: user.cpp: In function ‘int is(std::string, int, int, int)’: user.cpp:24:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<op.size();++i) { ^ user.cpp: In function ‘int eval(int, int)’: user.cpp:41:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int t = 0;t < ops.size();++t) { ^ user.cpp: In function ‘int make(std::string, int, int)’: user.cpp:37:1: warning: control reaches end of non-void function [-Wreturn-type] } ^