MatrixMultiply.cs

using System;

namespace CSharpStudy1
{
	static class LinearAlgebra
	{
		public static int[,] Multiply(int[,] mat1, int[,] mat2)
		{
			if (mat1.GetLength (1) != mat2.GetLength (0)) {
				Console.WriteLine ("Error: trying to calculate two matrices with incompatible size");
				return null;
			}
			int[,] answer = new int[mat1.GetLength (0), mat2.GetLength (1)];
			for (int i = 0; i < mat1.GetLength (0); i++) {
				for (int k = 0; k < mat1.GetLength (1); k++) {
					for (int j = 0; j < mat2.GetLength (0); j++) {
						answer [i, k] += mat1 [i, j] * mat2 [j, k];
					}
				}
			}
			return answer;
		}
		public static void printMatrix(int[,] mat)
		{
			for (int i = 0; i < mat.GetLength (0); i++) {
				for (int j = 0; j < mat.GetLength (1); j++) {
					Console.Write ("[ {0}, {1} ] : {2} ", i, j, mat [i, j]);
				}
				Console.WriteLine ();
			}
			Console.WriteLine ();
		}
	}
	static class MainClass
	{
		static void Main (string[] args)
		{
			int[,] mat1 = new int[2, 2] { { 10, 5 }, { 5, 10 } };
			int[,] mat2 = new int[2, 2] { { 3, 4 }, { 3, 4 } };
			int[,] result = LinearAlgebra.Multiply (mat1, mat2);
			LinearAlgebra.printMatrix (result);
		}
	}
}