FOREACH

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication5
{
    public partial class Form1 : Form
    {
        int[,] kunder = new int[10,3];
        public Form1()
        {
            InitializeComponent();
        }

        private void btnOpdater_Click(object sender, EventArgs e)
        {
            int kunde = int.Parse(txtKunde.Text);
            int saldo = int.Parse(txtSaldo.Text);

            kunder[kunde,0] = saldo;
        }

        private void btnTotal_Click(object sender, EventArgs e)
        {
            int saldo = 0;

            //for (int i = 0; i < 10; i++)
            //{
            //    saldo = saldo + kunder[i];
            //}

            foreach (int element in kunder)
            {
                saldo = saldo + element;
            }

            lblTotal.Text = saldo.ToString();
        }
    }
}