Compilare: main.cpp: In function 'int main()': main.cpp:41:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<s.length();i++) ~^~~~~~~~~~~ main.cpp:47:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i<s.length() && isdigit(s[i])) ~^~~~~~~~~~~ main.cpp: In function 'int calc(char, int, int)': main.cpp:18:1: warning: control reaches end of non-void function [-Wreturn-type] } ^