Compilare: main.cpp: In function 'void find_substr(std::__cxx11::string, int (&)[2000009])': main.cpp:12:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < s.length(); ++i) { ~~^~~~~~~~~~~~ main.cpp:18:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (R < s.length() && s[R] == s[R - i]) ~~^~~~~~~~~~~~ In file included from /usr/include/c++/6/cassert:44:0, from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:33, from main.cpp:1: main.cpp: In function 'int main()': main.cpp:44:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] assert(j < a.length() + b.length() + 1); ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~