What is $ _ SESSION used here?

What is $ _ SESSION used here? How can I use this calculator to enable the session before the session, but I have not set $ _ SESSION? why is session used here?

     
  Simple computer      
  

Reply to discussion (solution)

This page is useless.

It is useful if you need to display results on other pages.

This page is useless.

It is useful if you need to display results on other pages.

This is two pages. I wrote the code together. I tried to run the code normally. why is $ _ SESSION used here?

One page
$ _ SESSION ['Rs '] = $ rs;
Another page
Echo: '. $ _ SESSION ['Rs'];

This enables cross-page value transfer.

$ _ SESSION is used to pass values between pages.

One page
$ _ SESSION ['Rs '] = $ rs;
Another page
Echo: '. $ _ SESSION ['Rs'];

This enables cross-page value transfer.

$ _ SESSION ['Rs '] = $ rs;
Echo: '. $ _ SESSION ['Rs'];
Are these two sentences not on the same page?

One page
$ _ SESSION ['Rs '] = $ rs;
Another page
Echo: '. $ _ SESSION ['Rs'];

This enables cross-page value transfer.

The session is useless here. if I have gone all of them, I can also run it to pass the value through post.

This page is useless.

It is useful if you need to display results on other pages.

You're right. it's useless here.

You said it all.This is two pages, but the code is written together.
You have changed people's code and asked them what they mean. Don't you think it's strange?