Compilare: user.cpp: In function ‘void prefix_function()’: user.cpp:13:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 1; i < a.size(); i++) { ^ user.cpp: In function ‘void match()’: user.cpp:26:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < b.size(); i++) { ^ user.cpp:32:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k == a.size()) { ^ user.cpp: In function ‘int main()’: user.cpp:49:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < sol.size() && i < 1000; i++) { ^