Compilare: user.cpp: In function ‘int main()’: user.cpp:34:22: warning: statement has no effect [-Wunused-value] for(i;i<n;i++) ^ user.cpp:36:21: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[n]=NULL; ^ user.cpp:42:18: warning: NULL used in arithmetic [-Wpointer-arith] if(s[0]==NULL) ^ user.cpp:8:15: warning: unused variable ‘a’ [-Wunused-variable] int n,i,j,a,t=0; ^