The first is to make a copy and pass it in. The change of function does not affect the original value. (value transfer)

The second incoming is a pointer to int, and the subsequent operations are counted as pointers. (address delivery)

The third is direct transfer, and the change of function will also change the original value. (by reference)

Finally, no comments. It doesn't matter how many times you ask. There is no hint to comment on me here. It's hard to say if you see me more often.