How to subtract total of each row in C# matrix from constant number and sum the result?

Your code is already correct, you are just not showing correct values, here is the modified code (Magic Constant =13 here)

using System;

namespace MatrixSubtract
{
    class Program
    {
        static void Main(string[] args)
        {
            int[,] t = new int[,] { 
                { 4, 9, 2 },
                { 3, 5, 7 },
                { 8, 1, 5 }
            };

            int[] rowSum = new int[t.GetLength(0)],
            colSum = new int[t.GetLength(1)];

            int sum = 0;
            int magiconst = 13;
            int cons = 0;
            // Get the sum of each row and each column
            for (int r = 0; r < t.GetLength(0); r++)
            {
                for (int c = 0; c < t.GetLength(1); c++)
                {
                    rowSum[r] += t[r, c];
                    colSum[c] += t[r, c];
                }
                Console.WriteLine("Row sum: " + rowSum[r]);
                sum += Math.Abs(rowSum[r] - magiconst);
                Console.WriteLine("Row after subtraction: "
                    + Math.Abs(rowSum[r] - magiconst)
                    );

                //cons = cons + sum;               
                //Console.WriteLine(cons);
            }
            //show total sum here
            Console.WriteLine("All rows total: "+sum);
            Console.ReadKey();
        }
    }
}

Output

Above code shows sum of each row and subtraction from magic constant, then total sum of remainders.

Hi  Vikas_Jk  Thank you so much.