Compilare: main.cpp:43:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type] main() ^ main.cpp: In function 'int main()': main.cpp:48:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); i++) ~~^~~~~~~~~~ main.cpp:57:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < s.size() && s[i] >= '0' && s[i] <= '9') ~~^~~~~~~~~~ main.cpp:63:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i < s.size()) ~~^~~~~~~~~~ main.cpp: In function 'int calc(char, int, int)': main.cpp:41:1: warning: control reaches end of non-void function [-Wreturn-type] } ^