Compilare: main.cpp: In function 'void preproc()': main.cpp:11:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 1, len = 0; j < pat.size();) ~~^~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:24:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0, j = 0; i < s.size();) ~~^~~~~~~~~~ main.cpp:28:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j == pat.size()) ~~^~~~~~~~~~~~~ main.cpp:30:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] else if (i < s.size() && pat[j] != s[i]) ~~^~~~~~~~~~ main.cpp:30:17: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses] else if (i < s.size() && pat[j] != s[i]) ^