How to add/update SharePoint person/group field from Object model

While adding/updating the person/group field, we need to take care, because it’s required to be in specific format like value must be ID;#Name when assigning value.

Example code:
using (SPSite site = SPContext.Current.Site)
{
using (SPWeb web = site.OpenWeb())
{
try
{

web.AllowUnsafeUpdates = true;
string loginName = "domainname\\username";
SPUser theUser = web.SiteUsers[loginName];
SPList theList = (SPList)web.Lists["firstcustomlist"];
SPListItem theItem = theList.GetItemById(1);

theItem["usercol"] = theUser.ID.ToString() + ";#" + theUser.Name;
theItem.Update();
theList.Update();
}
catch (Exception ex)
{
string msg = ex.Message;
}
}
}