Named And Optional Parameters In C#

Option 1: Using Default Values

It is the common way to implement Optional Parameters. Here we need to set the default values of the parameters in the method definition. In the following code snippet, secondNumber default value is “0”. So we can pass one parameter to the method only and the complier will assume the second parameter value “0”. The method will return the result as “12”.

namespace ConsoleApp2  
{  
    public class MyDemo  
    {  
        public int AddNumber(int firstNumber, int secondNumber = 0)  
        {  
            return firstNumber + secondNumber;  
        }  
  
  
        public void MainMethod()  
        {  
            AddNumber(12);  
        }  
    }  
}

VisualStudio IntelliSense uses Square bracket to indicate Optional Parameters. It is shown in the following figure:

Figure 1: VisualStudio shows IntelliSense to implement Optional Parameter

Note: Default values always need to define in the end of the parameters list.

Option 2: Using OptionalAttribute

There is another way to implement Optional Parameters, i.e., using the Optional Attribute. To implement this, we need to import System.Runtime.InteropServices namespace. Then we need to add “Optional” keyword surrounded with the square bracket in the front of the method definition parameter. The “Optional” keyword is defined in the “Runtime.InteropServices” namespace.

In the following example, I define the second parameter (secondNumber) as optional; Compiler will consider “0” as default value. Optional attribute always need to be defined in the end of the parameters list.

Here is the complete code:

using System.Runtime.InteropServices;  
  
namespace ConsoleApp2  
{  
    public class MyDemo  
    {  
        public int AddNumber(int firstNumber, [Optional] int secondNumber)  
        {  
            return firstNumber + secondNumber;  
        }  
  
        public void MainMethod()  
        {  
            AddNumber(12);  
        }  
    }  
} 

Option 3: Using Method Overloading

One more ways we can implement optional parameters is using method overloading. Method overloading allows us to create multiple definitions of same method with different parameters. If you're new to method overloading, read Method Overloading In C#.

In the following code, we've defined two methods with same names (AddNumber) but different number of parameters. First, AddNumber() method takes only one parameter and second AddNumber() method takes two parameters. When we call AddNumber() method with one parameter only, the compiler will execute the first AddNumber() method. And similarly when we pass two parameters, the compiler will execute the second AddNumber() method.

Here is the complete code:

namespace ConsoleApp2  
{  
    public class MyDemo  
    {  
        public int AddNumber(int firstNumber)  
        {  
            return firstNumber;  
        }  
  
        public int AddNumber(int firstNumber, int secondNumber)  
        {  
            return firstNumber + secondNumber;  
        }          
  
        public void MainMethod()  
        {  
            AddNumber(12);  
            AddNumber(12, 13);  
        }  
    }  
}

Option 4: Using Params Keyword.

Using params, we can pass a number of parameters to a method and implement optional parameters concept.

There are some restrictions using the params keyword:

• You can only use the params keyword for one parameter in your method declaration.
• Params must be always the last parameter in method.

More on this visit Using Params in C#.

In the following example, numbers is the second parameter of AddNumber(), which is of type Integer Array type using “params”. The array items can be accessed using the array items index.

You can see, we have three different calls of the AddNumber method and values are read back and added to the result. In the first call, we call AddNumber() with one parameter(12) only and the result is 12. In the second call, we call AddNumber() with two parameters(12, 13). The result will be 25. In the third case, we pass three parameters (12,13,14). The result will be 39.

Here is the C# complete code example:

namespace ConsoleApp2  
{  
    public class MyDemo  
    {  
        public int AddNumber(int firstNumber, params int[] numbers)  
        {  
            int temp = 0;  
            foreach (int tempNum in numbers)  
            {  
                temp += tempNum;  
            }  
            return temp + firstNumber;  
        }  
  
        public void MainMethod()  
        {  
            AddNumber(12); // Result: 12  
            AddNumber(12, 13); // Result: 25  
            AddNumber(12, 13, 14); // Result: 39  
        }  
    }  
} 

Conclusion

In this article, we discussed Named and Optional Parameters in C#. We also saw different examples of these features of C#.