رمز Code:
private void button2_Click(object sender, EventArgs e)
{
string numberone;
string numbertwo;
string total;
numberone = txt1.Text;
numbertwo = txt2.Text;
total = numberone + numbertwo;



MessageBox.Show(total);

}

رمز Code:
private void button2_Click(object sender, EventArgs e)



{
double numberone, numbertwo;
numberone = double.Parse(txt1.Text);
numbertwo = double.Parse(txt2.Text);
MessageBox.Show((numberone + numbertwo).ToString());

}