Compilare: user.cpp: In function ‘void backtr(int)’: user.cpp:64:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=st[vf-1]+1; i<=v.size(); ++i) ^ user.cpp: In function ‘int main()’: user.cpp:90:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < v.size() - 1; ++i) { ^ user.cpp:91:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = i + 1; j < v.size(); ++j) { ^