C# | Add key and value into StringDictionary

StringDictionary.Add(String, String) method is used to add an entry with the specified key and value into the StringDictionary.

Syntax:

public virtual void Add (string key, string value);

Parameters:

key: It is the key of the entry which is to be added.
value: It is the value of the entry which is to be added. The value can be null.

Exceptions:

ArgumentNullException : If the key is null.
ArgumentException : It is an entry with the same key already exists in the StringDictionary.
NotSupportedException : If the StringDictionary is read-only.

Below programs illustrate the use of StringDictionary.Add(String, String) method:

Example 1:

// C# code to add key and value 
// into the StringDictionary 

using System; 

using System.Collections; 

using System.Collections.Specialized; 

class GFG { 

    // Driver code 

    public static void Main() 

    { 

        // Creating a StringDictionary named myDict 

        StringDictionary myDict = new StringDictionary(); 

        // Adding key and value into the StringDictionary 

        myDict.Add("A", "Apple"); 

        myDict.Add("B", "Banana"); 

        myDict.Add("C", "Cat"); 

        myDict.Add("D", "Dog"); 

        myDict.Add("E", "Elephant"); 

        // Displaying the keys and values in StringDictionary 

        foreach(DictionaryEntry dic in myDict) 

        { 

            Console.WriteLine(dic.Key + "  " + dic.Value); 

        } 

    } 
}

Output:

d  Dog
b  Banana
c  Cat
e  Elephant
a  Apple

Example 2:

// C# code to add key and value 
// into the StringDictionary 

using System; 

using System.Collections; 

using System.Collections.Specialized; 

class GFG { 

    // Driver code 

    public static void Main() 

    { 

        // Creating a StringDictionary named myDict 

        StringDictionary myDict = new StringDictionary(); 

        // Adding key and value into the StringDictionary 

        myDict.Add("A", "Apple"); 

        myDict.Add("B", "Banana"); 

        myDict.Add("C", "Cat"); 

        myDict.Add("D", "Dog"); 

        // It should raise "ArgumentException" 

        // as an entry with the same key 

        // already exists in the StringDictionary. 

        myDict.Add("C", "Code"); 

        // Displaying the keys and values in StringDictionary 

        foreach(DictionaryEntry dic in myDict) 

        { 

            Console.WriteLine(dic.Key + "  " + dic.Value); 

        } 

    } 
}

Runtime Error:

Unhandled Exception:
System.ArgumentException: Item has already been added. Key in dictionary: ‘c’ Key being added: ‘c’

Note:

The key is handled in a case-insensitive manner i.e, it is translated to lowercase before it is added to the string dictionary.
This method is an O(1) operation.

Reference: