Compilare: user.cpp: In function ‘int main()’: user.cpp:101:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < v.size()-1; ++i){ ^ user.cpp: In function ‘std::pair<nod*, char*> parse_expression(char*)’: user.cpp:25:80: warning: ‘left’ may be used uninitialized in this function [-Wmaybe-uninitialized] op_nod(nod *l, nod *r, const char op): left_nod(l), right_nod(r), operation(op){} ^ user.cpp:58:7: note: ‘left’ was declared here nod* left; ^