Compilare: user.cpp: In function ‘int cb(int, int)’: user.cpp:21:5: warning: unused variable ‘a’ [-Wunused-variable] int a; ^ user.cpp: In function ‘int main()’: user.cpp:37:6: warning: unused variable ‘a’ [-Wunused-variable] {int a; ^ user.cpp:38:5: warning: unused variable ‘n’ [-Wunused-variable] int n=1,x; ^ user.cpp:38:9: warning: unused variable ‘x’ [-Wunused-variable] int n=1,x; ^