Compilare: user.cpp: In function ‘void back(int, int)’: user.cpp:83:11: warning: unused variable ‘r’ [-Wunused-variable] int i,r; ^ user.cpp: In function ‘int main()’: user.cpp:105:9: warning: unused variable ‘a’ [-Wunused-variable] int a,i; ^ user.cpp:105:11: warning: unused variable ‘i’ [-Wunused-variable] int a,i; ^