You string may be smaller than 30 characters
Please run this code
HTML
<asp:Repeater ID="Repeater1" runat="server">
<ItemTemplate>
<span class="name" style="text-align: left; font-family: Arial; color: #0094DA; font-size: 14pt">
<%#Eval("LongString").ToString().Length >= 30 ? Eval("LongString").ToString().Substring(0, 30) : Eval("LongString").ToString()%></span>
</ItemTemplate>
</asp:Repeater>
Namespace
using System.Data;
C#
protected void Page_Load(object sender, EventArgs e)
{
DataTable dt = new DataTable();
dt.Columns.Add("LongString",typeof(string));
dt.Rows.Add("Suppose i am having 25 character length string and I want to bind only first 15 character of that string into the label control. ");
this.Repeater1.DataSource = dt;
this.Repeater1.DataBind();
}