Str Function ...

one of the problems to convert a program to function is use of string functions...
is there anyway to use these functions and convert program to function or not?

one of the problems to convert a program to function is use of string functions...
is there anyway to use these functions and convert program to function or not?

In short: NO. There is an AddIn that "converts" a program to a function, but it simply changes the header of the file; it doesn't work as expected, and it has strong limitations. This is because function support in CP Basic is extremely limited (I can say, "primitive").
My personal opinion is that, if you need real functions (supporting recursion etc), you should switch to CPLua, and forget CP Basic once and for all.

In short: NO. There is an AddIn that "converts" a program to a function, but it simply changes the header of the file; it doesn't work as expected, and it has strong limitations. This is because function support in CP Basic is extremely limited (I can say, "primitive").
My personal opinion is that, if you need real functions (supporting recursion etc), you should switch to CPLua, and forget CP Basic once and for all.

but the important think is to use funcyions in main calculator screen

but the important think is to use funcyions in main calculator screen

As far as I know, and I don't thik I'm wrong, you can only use CPBasic functions from the "Main" application, which means that you have very limited function support. I can say that you don't have function support at all - structures of one (and only one) statement cannot be called "functions". Inversely, though, you can use CAS statements within CPLua. Compared to a tru PC CAS, this approach is not without disadvantages, but you will have true function and CAS support.