PHP static variable testing, beginner PHP static variable error analysis

The three values ​​in the book are 1, 2, and 3 respectively However, the actual result is that it cannot be run, and the syntax is wrong. The reason for the post-check error is that the sentence $int+1."
" should be written as ($int+1)."
". After changing it, the program no longer reports an error. But the values ​​are 1, 1, 1; in fact, this is not difficult to explain. Although $int keeps adding 1, the result is not assigned to $int again. Why does $int increase?

Modify the code to the following to make it correct:

Note that the static keyword must be together with the assignment (php static static variable modifier usage), if it is written in the book

Error, the result after running is also 1, 1, 1