Compilare: main.cpp: In function 'std::__cxx11::string add(std::__cxx11::string, std::__cxx11::string)': main.cpp:16:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<c.size()-1;i++) ~^~~~~~~~~~~ main.cpp:18:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] c[i] += (i<a.size()?a[i]-'0':0) + (i<b.size()?b[i]-'0':0); ~^~~~~~~~~ main.cpp:18:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] c[i] += (i<a.size()?a[i]-'0':0) + (i<b.size()?b[i]-'0':0); ~^~~~~~~~~ main.cpp: In function 'std::__cxx11::string mult(std::__cxx11::string, int)': main.cpp:34:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0,val,p;i<a.size()+4;i++) ~^~~~~~~~~~~ main.cpp:36:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] val = (i<a.size() ? a[i]-'0' : 0)*nr + c[i]; ~^~~~~~~~~