Compilare: main.cpp: In function 'int main()': main.cpp:53:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < f.size(); ++i) ~~^~~~~~~~~~ main.cpp:54:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = i; j < f.size(); ++j) ~~^~~~~~~~~~ main.cpp:55:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = j; k < f.size(); ++k) ~~^~~~~~~~~~