foo.cpp: In function 'int main()':
foo.cpp:8:15: error: 'scanf' was not declared in this scope
  scanf("%d",&n);
               ^
foo.cpp:9:18: error: 'printf' was not declared in this scope
  printf("%d",a[n]);
                  ^
foo.cpp:6:6: warning: unused variable 'i' [-Wunused-variable]
  int i;
      ^