Check if the Hashtable contains a specific value in C#

To check if a Hashtable contains a specific value in C#, you use the ContainsValue() method. This method returns true if the specified value exists in the Hashtable, and false otherwise.

Syntax

Following is the syntax for checking if a Hashtable contains a specific value −

bool result = hashtable.ContainsValue(value);

Parameters

• value − The value to search for in the Hashtable. It can be null.

Return Value

Returns true if the Hashtable contains the specified value; otherwise, false.

Using ContainsValue() with Different Data Types

Example

using System;
using System.Collections;

public class Demo {
    public static void Main() {
        Hashtable hash = new Hashtable();
        hash.Add("1", "A");
        hash.Add("2", "B");
        hash.Add("3", "C");
        hash.Add("4", "D");
        hash.Add("5", "E");
        hash.Add("6", "F");
        hash.Add("7", "G");
        hash.Add("8", "H");
        hash.Add("9", "I");
        hash.Add("10", "J");
        
        Console.WriteLine("Hashtable Key and Value pairs...");
        foreach(DictionaryEntry entry in hash) {
            Console.WriteLine("{0} and {1}", entry.Key, entry.Value);
        }
        
        Console.WriteLine("\nChecking for specific values:");
        Console.WriteLine("Contains value 'H': " + hash.ContainsValue("H"));
        Console.WriteLine("Contains value 'Z': " + hash.ContainsValue("Z"));
        Console.WriteLine("Contains value 'A': " + hash.ContainsValue("A"));
    }
}

The output of the above code is −

Hashtable Key and Value pairs...
10 and J
1 and A
2 and B
3 and C
4 and D
5 and E
6 and F
7 and G
8 and H
9 and I

Checking for specific values:
Contains value 'H': True
Contains value 'Z': False
Contains value 'A': True

Checking for Values in a Name Database

Example

using System;
using System.Collections;

public class Demo {
    public static void Main() {
        Hashtable nameDatabase = new Hashtable();
        nameDatabase.Add("One", "Katie");
        nameDatabase.Add("Two", "John");
        nameDatabase.Add("Three", "Barry");
        nameDatabase.Add("Four", "Mark");
        nameDatabase.Add("Five", "Harry");
        nameDatabase.Add("Six", "Nathan");
        nameDatabase.Add("Seven", "Tom");
        nameDatabase.Add("Eight", "Andy");
        nameDatabase.Add("Nine", "Illeana");
        nameDatabase.Add("Ten", "Tim");
        
        Console.WriteLine("Name Database:");
        foreach(DictionaryEntry entry in nameDatabase) {
            Console.WriteLine("{0}: {1}", entry.Key, entry.Value);
        }
        
        Console.WriteLine("\nSearch Results:");
        Console.WriteLine("Contains 'Illeana': " + nameDatabase.ContainsValue("Illeana"));
        Console.WriteLine("Contains 'Sarah': " + nameDatabase.ContainsValue("Sarah"));
        Console.WriteLine("Contains 'Tom': " + nameDatabase.ContainsValue("Tom"));
    }
}

The output of the above code is −

Name Database:
One: Katie
Ten: Tim
Five: Harry
Three: Barry
Seven: Tom
Two: John
Four: Mark
Eight: Andy
Nine: Illeana
Six: Nathan

Search Results:
Contains 'Illeana': True
Contains 'Sarah': False
Contains 'Tom': True

ContainsValue() vs ContainsKey() Comparison

Conclusion

The ContainsValue() method provides an easy way to check if a Hashtable contains a specific value. While it's useful for value lookups, remember that it searches through all values sequentially, making it slower than key-based operations like ContainsKey().