C# | String.Contains() Method

In C#, String.Contains() is a string method. This method is used to check whether the substring occurs within a given string or not.

Syntax:

public bool Contains(string str)

Parameter:

str: It is the string which is to be checked. Type of this parameter is System.String.

Return Value: It returns the boolean value. If substring exists in string or value is the empty string (“”), then it returns True, otherwise returns False.

Exception: This method can give ArgumentNullException if str is null.

Note: This method performs the case-sensitive checking. The search will always begin from the first character position of the string and continues until the last character position.

Below are the programs illustrate the Contains() Method.

Program 1:

// C# program to demonstrate the
// String.Contains() Method
using System;

class Geeks {

    // Main Method
    public static void Main()
    {

        // string type
        String str = "GeeksforGeeks";
        String substr1 = "for";
        String substr2 = "For";

        // using String.Contains() Method
        Console.WriteLine(str.Contains(substr1));

        // Here case-sensitive comparison
        // And substr2 value is 'For'
        // So its return false
        Console.WriteLine(str.Contains(substr2));
    }
}

Output:

True
False

Program 2: To determine whether a substring is present in a string using ordinal comparison and case-insensitive ordinal comparison.

// C# program to illustrate the
// String.Contains() Method using
// ordinal comparison and case-
// insensitive ordinal comparison
using System;

public static class StringExtensions {

    // defines a String extension method
    // which includes a StringComparison parameter
    public static bool Contains(this String str,
                                String substr,
                                StringComparison cmp)
    {
        if (substr == null)
            throw new ArgumentNullException("substring substring",
                                            " cannot be null.");

        else if (!Enum.IsDefined(typeof(StringComparison), cmp))
            throw new ArgumentException("comp is not a member of",
                                        "StringComparison, comp");

        return str.IndexOf(substr, cmp) >= 0;
    }
}

// Driver Class
class Geeks {

    // Main Method
    public static void Main()
    {
        String str = "GeeksforGeeks";
        String substr = "FOR";

        // For Ordinal
        StringComparison comp = StringComparison.Ordinal;
        Console.WriteLine("For {0:G}: {1}", comp,
                          str.Contains(substr, comp));

        // for OrdinalIgnoreCase
        comp = StringComparison.OrdinalIgnoreCase;
        Console.WriteLine("For {0:G}: {1}", comp,
                          str.Contains(substr, comp));
    }
}

Output:

For Ordinal: False
For OrdinalIgnoreCase: True

Program 3: The following example determines whether the string “Computer” is a substring of given string. If it is found in the string, it also displays its starting position.

// C# program to demonstrate the
// String.Contains() Method
// along with the starting position
using System;

class Example {
    public static void Main()
    {
        string sub1 = "GeeksforGeeks is a Computer Science Portal";
        string sub2 = "Computer";

        // Check if the substring is
        // present in the main string
        bool b = sub1.Contains(sub2);

        Console.WriteLine("'{0}' is in the string '{1}': {2}",
                          sub2, sub1, b);
        if (b) {
            int index = sub1.IndexOf(sub2);
            if (index >= 0)
                Console.WriteLine("{0} begins at character position {1}",
                                  sub2, index + 1);
        }
    }
}

Output:

'Computer' is in the string 'GeeksforGeeks is a Computer Science Portal': True
Computer begins at character position 20

Reference: https://msdn.microsoft.com/en-us/library/system.string.contains