Input string was not in a correct format?

Question

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 WindowsFormsApp3

{

public partial class Form1 : Form

{

static int start_x = 0, start_y = 0;

static int end_x = 0, end_y = 0;

Graphics g = null;

Pen p = new Pen(Color.Red);

static int my_angle = 0, my_lenght = 0, my_increment = 0, num_lines = 0;

private void textBox2_TextChanged(object sender, EventArgs e)

{

}

public Form1()

{

InitializeComponent();

start_x = canvas.Width / 2;

start_y = canvas.Height / 2;

}

private void drawLines()

{if(String.IsNullOrWhiteSpace(angle.Text))

my_angle = my_angle + Int32.Parse(angle.Text);

my_lenght = my_lenght + Int32.Parse(increment.Text);

end_x = (int)(start_x + Math.Cos(my_angle* .017453292519) * my_lenght);

end_y = (int)(start_y + Math.Sin(my_angle* .017453292519) * my_lenght);

Point[] points = { new Point(start_x, start_y), new Point(end_x, end_y) };

start_y = end_y;

start_x = end_x;

g.DrawLines(p, points);

}

private void button1_Click(object sender, EventArgs e)

{

my_angle = Int32.Parse(angle.Text);

my_lenght = Int32.Parse(lenght.Text);

my_increment = Int32.Parse(increment.Text);

start_x = canvas.Width / 2;

start_y = canvas.Height / 2;

canvas.Refresh();

}

private void canvas_Paint(object sender, PaintEventArgs e)

{

g = canvas.CreateGraphics();

my_lenght = Int32.Parse(lenght.Text);

p.Width = 1;

for (int i = 0; i < Int32.Parse(nrlinii.Text);i++)

drawLines();

}

}

}

This is my code,the error ocurs at my_angle = Int32.Parse(angle.Text);

There is a string value in angle.Text,i have no idea why it would not work.