using an array in a custom formula in crystal reports xi

Question

I have a formula which is working; the formula uses an array. I tried to extract the formula to create a custom formula but now get an error in the syntax.

I am wondering if the array is causing the problem as the error is on the line:

last_element_current:=val(sc_array[1]) + 1;

and the error is: the ) is missing and highlights the variable sc_array before the index [1].