Local variables and global variables

After the loop, I is not recognized for I, so here I only action in the FOR statement I

Because the blue and red definitions are the same, the external blue I is shielded from the for, but the outside I only recognize the blue I

Global variables

So a global variable can be used by any function.

If we write the global variable in the back, it will go wrong!

We're going to use extern

That's it.

To make each function as single as possible, only one function is implemented

Local variables and global variables