matrix-multiplication.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MatrixMultiplying
{
    class Program
    {
        static void Main(string[] args)
        {
            Matrix m1 = new Matrix(new int[,]
            {
                { 1, 2, 3 },
                { 4, 5, 6 }
            });

            Matrix m2 = new Matrix(new int[,]
            {
                { 6, 5 },
                { 4, 3 },
                { 2, 1 },
            });

            Matrix m3 = new Matrix(new int[,]
            {
                { 1, 2, 3 }
            });

            Matrix m4 = new Matrix(new int[,]
            {
                { 13, 9, 7, 15 },
                { 8, 7, 4, 6 },
                { 6, 4, 0, 3 },
            });

            Console.WriteLine(m1);
            Console.WriteLine(m2);

            var m1m2 = m1.Times(m2);
            var m2m1 = m2.Times(m1);
            var m3m4 = m3.Times(m4);

            Console.WriteLine(m1m2);
            Console.WriteLine(m2m1);
            Console.WriteLine(m3m4);
        }
    }

    class Matrix
    {
        private int[,] nums;
        public Matrix(int[,] nums)
        {
            this.nums = nums;
        }

        public Matrix Times(Matrix other)
        {
            var result = new int[nums.GetLength(0), other.nums.GetLength(1)];

            for (int y = 0; y < nums.GetLength(0); y++)
            {
                for (int x = 0; x < other.nums.GetLength(1); x++)
                {
                    for (int i = 0; i < nums.GetLength(1); i++)
                    {
                        result[y, x] += nums[y, i] * other.nums[i, x];
                    }
                }
            }

            return new Matrix(result);
        }

        public override string ToString()
        {
            var sb = new StringBuilder();
            for (var i = 0; i < nums.GetLength(0); i++)
            {
                for (var j = 0; j < nums.GetLength(1); j++)
                {
                    sb.Append(nums[i, j] + " ");
                }
                sb.Append("\n");
            }
            return string.Join("\n", sb.ToString().Split('\n').Select(e => e.Trim()));
        }
    }
}