Compilare: main.cpp: In function 'std::__cxx11::string solve()': main.cpp:15:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(it >= s.size()) ~~~^~~~~~~~~~~ main.cpp:18:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(it < s.size() && s[it] >= 'a' && s[it] <= 'z') ~~~^~~~~~~~~~ main.cpp:24:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(it >= s.size()) ~~~^~~~~~~~~~~ main.cpp:31:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(it < s.size() && s[it] >= '0' && s[it] <= '9') ~~~^~~~~~~~~~ main.cpp:72:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(it >= s.size() || s[it] == ']' || s[it] == ')' || s[it] == '*') ~~~^~~~~~~~~~~ main.cpp: At global scope: main.cpp:78:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type] main() ^