Compilare: user.cpp: In function ‘bool eval(std::string)’: user.cpp:22:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<exp.size();i++) ^ user.cpp:21:11: warning: unused variable ‘j’ [-Wunused-variable] int i,j; ^ user.cpp: In function ‘int main()’: user.cpp:50:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=0;j<strlen(s)-1;j++) ^