Compilare: user.cpp: In function ‘void tr(std::vector<std::vector<int> >&, int)’: user.cpp:26:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j = 0;j < v[i].size();++j) ^ user.cpp: In function ‘int main()’: user.cpp:54:6: warning: unused variable ‘sum’ [-Wunused-variable] int sum = 0, i, j; ^ user.cpp:54:15: warning: unused variable ‘i’ [-Wunused-variable] int sum = 0, i, j; ^ user.cpp:54:18: warning: unused variable ‘j’ [-Wunused-variable] int sum = 0, i, j; ^