Compilare: user.cpp: In function ‘int main()’: user.cpp:21:18: warning: statement has no effect [-Wunused-value] for(i;i<n;i++) ^ user.cpp:25:17: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[n]=NULL; ^ user.cpp:29:14: warning: NULL used in arithmetic [-Wpointer-arith] if(s[0]==NULL) ^ user.cpp:8:9: warning: unused variable ‘t’ [-Wunused-variable] int t,n,i; ^