I Awais,

If I understood well your question, I think a good option is to use pointers of structures.

You first declare and initialize (with a calloc for example) a pointer on a structure. And this structure contains all the variables you need in your function, the inputs and the outputs.

In your main program, you attribute the values you want to the parameters that are inside the structure.

Then, the entry of the function is the pointer on the structure. Thus, in the function, you can access all the variables that are defined inside your structure. And also access them out of the function.

I hope it helped!

Julien.

Thankyou Julien

In C you may pass parameters "by reference": for example take the function

   void swap(int *x, int *y) { int t = *x; *x = *y; *y = t; }

You may use this function to swap the value of two variables, like in

...

   int a = 1, b = 2;

   swap(&a, &b);   /* &a is the address of variable a. */

   /* Now the value of a is 2 and the value of b is 1. */

...

So if you pass the address of variables instead of their values, the function will actually modify the variable's content and after returning from the function the modified values will be available to the main function.

In this way you can get as many outputs as you want from a function.

Hope this help!

To expand the previous answers:

1. define a struct that holds everything you need for the filter: internal variables (e.g. internal filter value, filter state etc.) Your struct  may even have storage for the input and the output value. (Why pass them as separate arguments when you can as well store them within the filter structure). Example: #typedef struct { .... } butterworth_s;

2. Write the filter function - having an argument of type address-of-struct:

   butterworth(butterworth_s *this_channel).

   References to the elements of butterworth_s will typically look like 'this_channel->input".

3. create an instance of this struct for each channel where you want to apply this filter:

    butterworth_s  filter_a, filter_b, filter_c, ...;

4. When you want to perform the filter function:

   copy the latest value to the corresponding structure: filter_a.input = a;   call the filter function with the reference to the structure: butterworth(&filter_a);

   (most compilers will as well accept the omission of the address operator '&' a structs are

   always passed by reference.)

If you have minimum knowledge about working with struct, the above might help to get things done.

Wish you success

Thankyou So much every body :)

use pointer of struct.