foeeach in c#

It is used on a collection and returns each element in order.
->foreach & for loop same work or function(print) but incase of foreach we can't modify in future .

sample code:

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        int[] marks = new int[] { 60, 70, 80 };
        foreach(int s in marks) 

        {
            Response.Write(s);
        }

    }
}