c# - How to find second occurrence of a substring in a string

String find second occurrence
string-find-second-occurrence.aspx

<%@ Page Language="C#" AutoEventWireup="true"%>

<!DOCTYPE html>  
<script runat="server"> 
    protected void Button1_Click(object sender, System.EventArgs e)  
    {
        //this section create a string variable.
        string plants = "Paper Birch. Red Birch. Bay Laurel. Silver Birch.";

        Label1.Text = "string of plants..................<br />";
        Label1.Text += plants+"<br />";

        //substring to find/search indexes/occurrences in string.
        string indexOfSubStringToFind = "Birch";

        int index = 0;
        int counter = 0;
        
        //find all indexes/occurrences of specified substring in string
        while ((index=plants.IndexOf(indexOfSubStringToFind, index)) != -1)
        {
            index++;
            counter++;
            //this line check second occurrence of search substring.
            if (counter == 2)
            {
                Label1.Text += "<br />Second occurrence of [Birch] found at index: " + index;
                break;
            }
        }
    }  
</script>  
  
<html xmlns="http://www.w3.org/1999/xhtml">  
<head id="Head1" runat="server">  
    <title>c# example - string find second occurrence</title>  
</head>  
<body>  
    <form id="form1" runat="server">  
    <div>  
        <h2 style="color:MidnightBlue; font-style:italic;">  
            c# example - string find second occurrence
        </h2>  
        <hr width="550" align="left" color="Gainsboro" />  
        <asp:Label   
            ID="Label1"   
            runat="server"  
            Font-Size="Large"
            >  
        </asp:Label>  
        <br /><br />
        <asp:Button   
            ID="Button1"   
            runat="server"   
            Text="string find second occurrence"  
            OnClick="Button1_Click"
            Height="40"  
            Font-Bold="true"  
            />  
    </div>  
    </form>  
</body>  
</html>
More c# examples