String manupulation

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 WindowsFormsApplication146
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnUpper_Click(object sender, EventArgs e)
        {
            string temp = txtIndTekst.Text;
            temp = temp.ToUpper();
            lblUdtekst.Text = temp;
        }

        private void btnLength_Click(object sender, EventArgs e)
        {
            string temp = txtIndTekst.Text;
            int længde = temp.Length;
            lblUdtekst.Text = længde.ToString();
        }

        private void btnSubString_Click(object sender, EventArgs e)
        {
            string temp = txtIndTekst.Text;
            int start = int.Parse(txtStart.Text);
            int antal = int.Parse(txtAntal.Text);

            temp = temp.Substring(start, antal);
            lblUdtekst.Text = temp;
        }
    }
}