string Split string Substring Length if all for int ListOfClients Coun

string l = s.Split(':')[0];
string m = s.Substring(l.Length + 2);
if (l == "all")
{
    for (int i = 0; i < ListOfClients.l.Count; i++)
    {
        ListOfClients.l[i].Write(m);                   
    }
}