«

Hi, I wrote some programs with friend classes but some of them work and
some of them don't work, can antbody help me? First, I want to know how
much it is useful in programming, Then I need links to learn about it
and finally if you can, help me!

wrote:
> Hi, I wrote some programs with friend classes but some of them work and
> some of them don't work, can antbody help me?

You have an error on line 42 of your program. Post a minimal,
compilable example that shows the behavior you don't like, tell us what
behavior you expected, and what you got.

> First, I want to know how
> much it is useful in programming, Then I need links to learn about it
> and finally if you can, help me!

It's as useful as any other part of the language.

Read your text book.

This sounds suspiciously like homework.

wrote:

> Hi, I wrote some programs with friend classes but some of them work and
> some of them don't work, can antbody help me?

Yes - first you need to fix the errors in your code, and then I expect
the classes will work properly. Please let us know if you need
additional help.

> First, I want to know how
> much it is useful in programming, Then I need links to learn about it
> and finally if you can, help me!

Now, I'm sure you checked the FAQ before posting, but just in case, I
expect you will find the following two references answer most or all of
your questions:

http://www.parashift.com/c++-faq-lite/friends.html

http://www.parashift.com/c++-faq-lit...t.html#faq-5.8

Good luck.

Best regards,

Tom