Compilare: user.cpp: In function ‘int main()’: user.cpp:21:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=2;i<=N;i++) ^ user.cpp:29:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j=1;j<=N;j++) ^ user.cpp:47:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=1;i<=N;i+=10) ^ user.cpp:17:15: warning: unused variable ‘l’ [-Wunused-variable] int i,j,k,l; ^