#774 – Passing an Array as an out Parameter

Like other reference types, you can use an array as an output parameter, using the out keyword.  The out keyword indicates that you must assign a value to the array before returning from the method.  Also, within the method, you cannot reference the array parameter before you assign a new value to it.

        static int FindFibsThrough(int numFibs, out int[] fibs)
            // Can't reference element of array
            //int i = fibs[0];

            // Can't assign to element of array
            //fibs[0] = 12;

            if (numFibs < 2)
                throw new Exception("Must return at least 2 numbers in sequence");

            // Must assign new value to array before we return
            fibs = new int[numFibs];

            fibs[0] = 0;
            fibs[1] = 1;
            int sum = 1;

            for (int i = 2; i < numFibs; i++)
                fibs[i] = fibs[i - 1] + fibs[i - 2];
                sum += fibs[i];

            return sum;

You must also use the out keyword when calling the method.

            int[] myFibs;
            int sum = FindFibsThrough(10, out myFibs);