Compilare: main.cpp: In function 'int main()': main.cpp:30:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (next_pos[i]<s.size() && next_pos[i]-i<=19) ~~~~~~~~~~~^~~~~~~~~ main.cpp:34:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (k=next_pos[i]+1;k<s.size() && k-i<=20;++k) ~^~~~~~~~~ main.cpp:38:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0;i<s.size();++i) ~^~~~~~~~~ main.cpp:44:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (next_pos[i]<s.size() && next_pos[i]-i<=19) ~~~~~~~~~~~^~~~~~~~~ main.cpp:48:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (k=next_pos[i]+1;k<s.size() && k-i<=20;++k) ~^~~~~~~~~