How do I create a GetAverage method for a 3x3 retangular array in C#?

Question

I am having trouble figuring this out. I need to put items in a 3x3 rectangular array and then average them. This is my code for putting the values in the array:

                    // Add Values to Rectangular Array
                    for (int i = 0; i < retailPrices.GetLength(0); i++)
                    {
                        for (int j = 0; j < retailPrices.GetLength(1); j++)
                        {
                            retailPrices[i, 0] = wholesaleCost;
                            retailPrices[i, 1] = markupPercentage;
                            retailPrices[i, 2] = futureValue;
                        }
                    }

This is my code for my GetAverage Method:

  private decimal GetAverage(decimal[,] retailPrices)
        {
            decimal sum = 0m;
            for (int i = 0; i < retailPrices.GetLength(0); i++)
            {
                for (int j = 0; j < retailPrices.GetLength(1); j++)
                {
                    sum += retailPrices[i, j];
                }
            }
            decimal average = sum / retailPrices.GetLength(0);
            return average;
        }

What is the correct way to do this? What am I doing incorrectly? Please correct my code.

Answer 1

To calculate the average of all nine values:

using System.Linq;
. . .
private decimal GetAverage( decimal[,] retailPrices )
{
   return retailPrices.Cast<decimal>( ).Average( );
}

Answer 2

You need to calc the size of the arrays.

   private decimal GetAverage(decimal[,] retailPrices) 
         { 
             decimal sum = 0m; 
             decimal count =0m; 
             for (int i = 0; i < retailPrices.Length; i++) 
             { 
                 count += retailPrices[i].Length; 
                 for (int j = 0; j < retailPrices[i].Length; j++) 
                 {
                     sum += retailPrices[i, j]; 
                 } 
             } 
             decimal average = sum / count; 
             return average; 
         }