Compilare: user.cpp: In function ‘int main()’: user.cpp:326:13: warning: unused variable ‘k’ [-Wunused-variable] int n,m,k=9; ^ user.cpp: In instantiation of ‘T lista<T>::operator[](int) [with T = char]’: user.cpp:312:13: required from ‘T stiva<T>::top() [with T = char]’ user.cpp:336:43: required from here user.cpp:204:16: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] return NULL; ^ user.cpp:206:12: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] return NULL; ^