Just Allow Numbers in a Textbox

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{

if (!char.IsNumber(e.KeyChar) & (Keys)e.KeyChar != Keys.Back & e.KeyChar != '.')
{
e.Handled = true;
}

}

Other basic example using TryParse

private void btn_Click(object sender, EventArgs e)
{

string nombre = textBox1.Text;
int Aux;

if (!int.TryParse(nombre, out Aux))
MessageBox.Show("just numbers");
}