You are converting both values to int and then dividing
so since int type does not return decimal value it is giving zero as output.
instead you convert the numbers to float, you will get the results.
try this
private void txtpresent_Leave(object sender, EventArgs e)
{
temp = (float.Parse(txtpresent.Text) / float.Parse(txtworkingdays.Text)*100);
txtpercentage.Text = temp.ToString();
}