Storing multiple function calls in an array

[waelt]

My function returns an int array with 2 values
Let's say, res[0] and res[1]

When I'm calling the array in a for loop for multiple times, and when I'm storing the results in another array, in each iteration the results are over-written with the new results.

If the first call returns [0,1] the array will store [0,1] at index [0] and [1], which is fine, but when I'm calling the function again, the new results are stored at the same indexes [0] and [1]
How can I avoid that?

Function Code:

     int[] MatrixMul(string subInput, int[,] key)
            {
                int[] result = new int[subInput.Length];
                for (int row = 0; row < key.GetLength(0); row++)
                {
                    for (int col = 0; col < key.GetLength(0); col++)
                    {
                       result[row]+= key[row, col] * AtoZ.IndexOf(subInput[col]);
                        
                    }
                    
                }
                return result;
            }

Calling Code:

 for (int i = 0; i < outPut.Length; i++)
                {
                    encChars = MatrixMul(outPut[i], key);
                }

I really need some advice, so I can call my function and store all the values in this array.