Computer Science Canada

Functions and Updating two values
Author:  EiCCA [ Wed Jun 14, 2006 11:43 am ]
Post subject:  Functions and Updating two values
There are two questions I have here in this topic

1) In C++, you can declare a function type as void, meaning it does not return a value. What is the term for this in Turing?

2) I have a situation where I need two variables in a funtion to update their values after the function closes.

For example:

code:

function asdf(x : int, y : int) : <void>
       x := 5
       y := 6
end asdf

put x
put y


In C++, you can do this using refrence paramaters, using the & beside the paramater name, however I do not know how this is done in Turing.

Help? Very Happy Thanks a lot
Author:  wtd [ Wed Jun 14, 2006 12:54 pm ]
Post subject: 
1. Such things are known as procedures in Turing.

2. You can do this in Turing by prefixing the parameter name with "var ". However, for such a simple case, there is a better approach. Simply link both variables into a single data type, then return that.

code:
type Point :
  record
    x, y : int
  end record


Or in C++ simply use the std::pair class as defined by the STL.
Author:  Tony [ Wed Jun 14, 2006 6:47 pm ]
Post subject: 
code:

function asdf(x : int, y : int) : <void>
       x := 5
       y := 6
end asdf

put asdf(1,2)

the above clearly doesn't work. X and Y are local variables.

What'd you'd need to do is pass the reference to the variable's address. Now you're getting into pointers and what not. Turing might actually have a similar syntax involving &, but I don't recall at the moment. Consult your F10 manual.

Raguardless, the best practice is to have the function return the updated values.
Author:  [Gandalf] [ Wed Jun 14, 2006 7:01 pm ]
Post subject: 
Tony, like wtd said you can get the pass by reference effect by prefixing the parameter name with "var", for example:
code:
procedure changeValue (var num : int)
    num += 5
end changeValue

var myValue : int := 7
put myValue
changeValue (myValue)
put myValue %outputs 12

Though yes, you could also return a type containing all your data.
Author:  Tony [ Wed Jun 14, 2006 7:03 pm ]
Post subject: 
ah. thx for pointing that out.

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