Please refer this code
TextBox1
<asp:TextBox ID="TextBox1" runat="server" />
<br />
TextBox2
<asp:TextBox ID="TextBox2" runat="server" />
C#
protected void Page_Load(object sender, EventArgs e)
{
string data = "10.03";
string[] splitData = data.Split('.');
TextBox1.Text = splitData[0];
TextBox2.Text = splitData[1];
}