private void button8_Click(object sender, EventArgs e)
        {
            string s1 = "The quick brown fox jumps over the lazy dog";
            string sub1 = "fox"; // "Fox";
          
            bool ignoreCaseSearchResult = s1.StartsWith(sub1,
                System.StringComparison.CurrentCultureIgnoreCase);
            if (ignoreCaseSearchResult)
            {
                int index = s1.IndexOf(sub1);
                if (index >= 0)
                    MessageBox.Show("НАЙДЕНО");
            }
            else
                MessageBox.Show("НЕ НАЙДЕНО");
        }

string s1 = "The quick brown fox jumps over the lazy dog";
string s2 = "fox";
bool b = s1.Contains(s2);
Console.WriteLine("'{0}' is in the string '{1}': {2}",
                s2, s1, b);
if (b) {
    int index = s1.IndexOf(s2);
    if (index >= 0)
        Console.WriteLine("'{0} begins at character position {1}",
                      s2, index + 1);
}
// This example displays the following output:
//    'fox' is in the string 'The quick brown fox jumps over the lazy dog': True
//    'fox begins at character position 17 

bool b = s1.StartsWith(sub1, System.StringComparison.CurrentCultureIgnoreCase);
            // b = "false" несмотря на то, что в обоих строках, например "fox" or  "Fox"

 var b = s1.Contains(sub1, StringComparison.CurrentCultureIgnoreCase);

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <ProjectView>ProjectFiles</ProjectView>
  </PropertyGroup>
</Project>