Compilare: main.cpp: In function 'int main()': main.cpp:19:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < s.size()) { ~~^~~~~~~~~~ main.cpp:27:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while('0' <= s[i] && s[i] <= '9' && i < s.size()) ~~^~~~~~~~~~ main.cpp:29:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i == s.size()) { ~~^~~~~~~~~~~ main.cpp:36:16: warning: array subscript has type 'char' [-Wchar-subscripts] coef[s[i]] += sgn * num; ^