Contains

using System;

/// <summary>
/// Returns a value indicating whether the specified <see cref="string"/> object occurs within the <paramref name="this"/> string.
/// A parameter specifies the type of search to use for the specified string.
/// </summary>
/// <param name="this">The string to search in</param>
/// <param name="value">The string to seek</param>
/// <param name="comparisonType">One of the enumeration values that specifies the rules for the search</param>
/// <exception cref="ArgumentNullException"><paramref name="this"/> or <paramref name="value"/> is <c>null</c></exception>
/// <exception cref="ArgumentException"><paramref name="comparisonType"/> is not a valid <see cref="StringComparison"/> value</exception>
/// <returns>
/// <c>true</c> if the <paramref name="value"/> parameter occurs within the <paramref name="this"/> parameter, 
/// or if <paramref name="value"/> is the empty string (<c>""</c>); 
/// otherwise, <c>false</c>.
/// </returns>
/// <remarks>
/// The <paramref name="comparisonType"/> parameter specifies to search for the value parameter using the current or invariant culture, 
/// using a case-sensitive or case-insensitive search, and using word or ordinal comparison rules.
/// </remarks>
public static bool Contains(this string @this, string value, StringComparison comparisonType)
{
    if (@this == null)
    {
        throw new ArgumentNullException("this");
    }

    return @this.IndexOf(value, comparisonType) >= 0;
}

// This example is based on the example from http://msdn.microsoft.com/en-us/library/ms224425.aspx
using System;

class Sample 
{
    public static void Main() 
    {
        // Define a string to search for.
        // U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
        string CapitalAWithRing = "\u00c5"; 
        
        // Define a string to search. 
        // The result of combining the characters LATIN SMALL LETTER A and COMBINING 
        // RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character 
        // LATIN SMALL LETTER A WITH RING ABOVE (U+00e5).
        string cat = "A Cheshire c" + "\u0061\u030a" + "t";
        
        StringComparison[] scValues = {
            StringComparison.CurrentCulture,
            StringComparison.CurrentCultureIgnoreCase,
            StringComparison.InvariantCulture,
            StringComparison.InvariantCultureIgnoreCase,
            StringComparison.Ordinal,
            StringComparison.OrdinalIgnoreCase };
            
        // Display the current culture because culture affects the result. For example, 
        // try this code example with the "sv-SE" (Swedish-Sweden) culture.
        Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
        Console.WriteLine("The current culture is \"{0}\" - {1}.", 
                        Thread.CurrentThread.CurrentCulture.Name,
                        Thread.CurrentThread.CurrentCulture.DisplayName);
                        
        // Display the string to search for and the string to search.
        Console.WriteLine("Search for the string \"{0}\" in the string \"{1}\"", 
                        CapitalAWithRing, cat);
        Console.WriteLine();
        
        
        foreach (StringComparison sc in scValues)
        {
            var isInString = cat.Contains(CapitalAWithRing, sc);
            Console.WriteLine("Comparison: {0,-28} Is In String?: {1}", sc, isInString);
        }
    }
}