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What is an Optional parameter in C#?
By default, all parameters of a method are required. A method that contains optional parameters does not force to pass arguments at calling time. It means we call method without passing the arguments.
The optional parameter contains a default value in function definition. If we do not pass optional argument value at calling time, the default value is used.
Thera are different ways to make a parameter optional.
Using Default Value
Example
using System;
namespace DemoApplication{
class Demo{
static void Main(string[] args){
OptionalMethodWithDefaultValue(5);
//Value2 is not passed as it is optional
OptionalMethodWithDefaultValue(5, 10);
//Value2 is passed
Console.ReadLine();
}
public static void OptionalMethodWithDefaultValue(int value1, int value2 = 5){
Console.WriteLine($"Sum is {value1 + value2}");
}
}
}Output
The output of the above code is
Sum is 10 Sum is 15
In the above example, the method OptionalMethodWithDefaultValue(int value1, int value2 = 5) value2 is having default value 5. So if no arguments is passed for value2 while calling it will take the default value 5 and if an argument is passed for value2 then the default value is overridden.
Using Optional Attribute
Example
using System;
using System.Runtime.InteropServices;
namespace DemoApplication{
class Demo{
static void Main(string[] args){
OptionalMethodWithDefaultValue(5);
OptionalMethodWithDefaultValue(5, 10);
Console.ReadLine();
}
public static void OptionalMethodWithDefaultValue(int value1, [Optional]int value2){
Console.WriteLine($"Sum is {value1 + value2}");
}
}
}Output
The output of the above code is
Sum is 5 Sum is 15
Here for the [Optional] attribute is used to specify the optional parameter.
Also, it should be noted that optional parameters should always be specified at the end of the parameters. For ex − OptionalMethodWithDefaultValue(int value1 = 5, int value2) will throw exception.
Example
using System;
namespace DemoApplication{
class Demo{
static void Main(string[] args){
OptionalMethodWithDefaultValue(5);
OptionalMethodWithDefaultValue(5, 10);
Console.ReadLine();
}
public static void OptionalMethodWithDefaultValue(int value1 = 5, int value2){
Console.WriteLine($"Sum is {value1 + value2}");
}
}
}Error − Optional Parameters must appear after all required parameters.
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