Compilare: user.cpp: In function ‘int main()’: user.cpp:77:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < sol.size(); i++) ^ user.cpp:33:9: warning: unused variable ‘i’ [-Wunused-variable] int i,j,k,len=0; ^ user.cpp:33:11: warning: unused variable ‘j’ [-Wunused-variable] int i,j,k,len=0; ^ user.cpp:33:13: warning: unused variable ‘k’ [-Wunused-variable] int i,j,k,len=0; ^