array adding int.

i++; // What's this doing here?
     // You're incrementing i, but haven't initialised it

if(i == 10){i == 0;} // Should be i=0 ?

array[i] = data;  // you're putting an uninitialised value from data into one element of array
                  // i was uninitialised, so it could be anything now
                  // (because of the preceding error, i could even be 10!)

data = 0;         // having just used data, you now initialise it!

for (a = 0; a < 10 ; a++)
	{data = data + array[i];} // you repeat this assignment 10 times
                                  // still using the undefined value of 'i' each time

I did post an error when I posted the

{i == 0;}

{i=0;}

It's hard to figure things out since you didn't specify any variable types.

i++;

if(i == 10){i == 0;}

array[i] = data;

data = 0;

for (a = 0; a < 10 ; a++)
	{data = data + array[i];}

unsigned int func (unsigned char data)
{
#define ARRAY_SIZE 10

static unsigned char ndx = 0;
static unsigned char array [ARRAY_SIZE] = { 0, };
static unsigned int array_ttl;

if (++i >= ARRAY_SIZE) i = 0;

array_ttl -= array[ndx]; // remove oldest data
array_ttl += data;       // add newest data
array[ndx] = data;       // add newest data to array

return (array_ttl);      // return total
or
return (array_ttl/ARRAY_SIZE);  // return average
}

for (a = 0; a < 10 ; a++)
	{data = data + array[i];}

data = data + array[i];

"The simulator was only updating the results when I minimized the maximized my window."

Have you checked 'Periodic Window Update' on the 'View' menu?

Why would you use

unsigned char array [ARRAY_SIZE]